Commonly used computer terminology

This is a brief list of some commonly used terms and expressions used by computer people. It is not an exhaustive list and many of the terms can be found in greater detail in the Wikipedia.

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term	meaning
Reaction	A predefined or expressive response to online content, such as a like, heart, laugh, surprise, sadness, or anger indicator.
read lock	A lock allowing multiple readers to access a resource while preventing conflicting modifications.
readelf	A Linux utility for displaying detailed information about ELF object files and executables.
real GID	The group ID identifying the primary group associated with the user who initiated a Unix process.
real UID	The user ID identifying the user who initiated a Unix process.
real-time scheduling	Operating-system scheduling designed to provide predictable timing behaviour for tasks with strict response or execution deadlines.
real-time system	A computing system in which correctness depends not only on the result of computation but also on producing that result within specified timing constraints.
realloc	A C standard-library function used to change the size of a previously allocated memory block.
reaping	The process by which a Unix parent process collects the exit status of a terminated child process, removing its remaining process-table entry.
rebase	A version-control operation that reapplies a sequence of changes onto a different base revision.
reboot	To restart a computer or operating system.
Recommendation Algorithm	An algorithm that selects and ranks content, accounts, products, or other material that an online service predicts may be relevant or interesting to a user.
recovery mode	A system startup option providing maintenance and troubleshooting facilities, commonly including tools for repairing filesystems, packages or configuration.
Recursion	A programming technique in which a function or procedure calls itself, normally with a condition that eventually stops the recursion.
recursion depth	The number of nested active recursive calls at a particular point during program execution.
recursive DNS	DNS resolution in which a resolver obtains the requested information on behalf of the client, potentially querying multiple authoritative servers.
redirection	A shell mechanism for changing where a command obtains input or sends output, commonly using files instead of the terminal.
redirection operator	A shell syntax element used to connect a command's standard input or output to a file or another descriptor.
reentrant	Describing code that can safely be called again before a previous invocation has completed, including from another execution context such as a signal handler or thread.
refactoring	The process of restructuring existing source code to improve its design, readability or maintainability without intentionally changing its externally observable behaviour.
reference	A programming-language mechanism representing or referring to another object, value or resource without necessarily containing the object itself.
reference counting	A memory-management technique in which an object keeps a count of references to it and can be reclaimed when that count reaches zero.
Regex	Regular Expression – a pattern used to search, match, extract or replace text according to defined rules.
register	A small, fast storage location inside a processor used to hold values, addresses, instruction information or other state during execution.
Registry	A hierarchical database used by Microsoft Windows to store system, hardware, application and user configuration information.
regression	A defect in which a previously working feature stops working correctly following a change to software or its environment.
regression test	A test performed to ensure that previously working functionality continues to work after software changes.
Regular Expression	A pattern used to search, match, validate or manipulate text according to specified rules.
relatime	A Linux filesystem mount option that reduces the frequency of access-time updates while retaining useful atime information.
Relational Database	A database that organises information into tables consisting of rows and columns, with relationships between tables commonly represented using keys.
Relational Database Management System	A DBMS that stores data using related tables and commonly provides SQL for querying and managing the data.
release build	A software build intended for distribution or production use, commonly using optimisation and omitting some debugging facilities.
release candidate	A software version considered sufficiently complete for release testing and potentially suitable for final release if no significant defects are discovered.
relocatable object	An object file containing machine code and data whose addresses have not yet been fully resolved and which can be combined with other object files by a linker.
relocation	The process of adjusting addresses in compiled or linked code when code or data is loaded or linked at a different address than originally assumed.
Remote Desktop	Technology that allows a user to interact with a computer remotely as though using its local display and input devices.
Remote Procedure Call	A mechanism that allows a program to request that a procedure be executed in another process or on another computer.
renice	A Unix utility used to change the scheduling nice value of an existing process.
REPL	Read-Eval-Print Loop – an interactive programming environment that repeatedly reads input, evaluates it, displays the result and waits for further input.
replay attack	An attack in which previously captured valid communication is transmitted again to cause an unintended or unauthorised action.
Reply (social media)	A response posted in connection with another user's post, message, or comment, usually forming part of a conversation or discussion.
Report (social media)	A user action that submits content, an account, or other activity to a service for review because it may violate rules, policies, or applicable law.
Repository	A storage location for files and their revision history, commonly used by version control systems such as Git.
repository mirror	A server containing a replicated copy of a software repository, usually provided to improve download performance or availability.
Repost	The act of publishing or sharing another user's existing content so that it can be seen by the republishing user's audience.
reproducible build	A build process in which the same source code and build inputs produce functionally or byte-for-byte identical output, depending on the definition used.
resampling	The process of changing the pixel dimensions or sampling resolution of a digital image.
rescue mode	A restricted operating mode used for repairing or maintaining a system when normal startup or operation is not possible.
REST	Representational State Transfer – an architectural style commonly used for designing web APIs around resources and standard HTTP operations.
restore	The process of recovering files, data or an entire system from a backup or other preserved copy.
return code	A numerical value returned by a program or function to indicate the result of an operation. In Unix and Linux command-line usage it commonly refers to a process exit status.
return value	The value produced by a function when it completes and returns control to its caller.
Reverse DNS	The process of using DNS to determine a hostname associated with an IP address, normally through a PTR record.
Reverse Proxy	A proxy server positioned in front of one or more backend servers that receives client requests and forwards them to appropriate backend services.
reverse proxy cache	A reverse proxy that stores responses from backend or origin servers and can subsequently serve cached responses directly to clients.
reverse tunnel	A network tunnel in which a connection initiated from one system allows another system to reach services through that connection, commonly implemented using SSH remote forwarding.
RFC	Request for Comments – a series of technical documents used to publish Internet standards, protocols, specifications, proposals and related information.
RFC1918	A set of IPv4 address ranges reserved for private networks: 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16.
RGB	Red, Green and Blue – a colour model in which colours are represented by combining different intensities of red, green and blue components.
RGBA	Red, Green, Blue, Alpha – an RGB colour representation with an additional alpha channel describing transparency or opacity.
RIP	Routing Information Protocol – an older distance-vector routing protocol using hop count as its principal routing metric.
RJ45	A commonly used modular connector associated with Ethernet network cabling. The technically correct designation for the connector used by Ethernet is 8P8C, although RJ45 is the term most commonly used.
rlimit	A family of Unix process resource limits controlling quantities such as open files, process address space and CPU time.
Rlogin	Remote Login – an older Unix networking protocol allowing a user to log into another computer over a network.
rm	Remove – a Unix and Linux command used to delete files and, with appropriate options, directories.
rmdir	Remove Directory – a Unix and Linux command used to remove empty directories.
roaming	The process of a wireless client moving between access points while maintaining network connectivity.
Robots.txt	A text file placed at the root of a website containing rules intended to tell automated web crawlers which areas of the site they should or should not access.
rolling release	A software-distribution model in which updates are continuously delivered rather than being grouped into distinct major releases.
ROM	Read-Only Memory – non-volatile memory traditionally used to store data or instructions that should remain available when power is removed.
Root	The administrative superuser account on Unix-like operating systems, normally having unrestricted access to the system.
Root Directory	The top-level directory of a Unix-like filesystem, represented by a single forward slash.
root filesystem	The filesystem containing the top-level directory of a Unix or Linux system, conventionally represented by /.
Root User	The Unix or Linux superuser account with extensive privileges over the operating system.
rootkit	Software designed to maintain privileged access to a system while concealing its presence or activities.
route	A path through one or more networks used to deliver packets towards their destination.
Router	A network device that forwards data packets between different networks, such as between a home network and the Internet.
routing table	A data structure maintained by a networked computer or router containing information used to determine where packets should be sent.
rpath	A path embedded in a binary that tells a dynamic loader where to search for shared libraries required by that binary.
RPM	A package format and package-management system commonly associated with Linux distributions such as Red Hat Enterprise Linux and Fedora.
RSA	A public-key cryptographic algorithm based on the computational difficulty of factoring large integers, historically widely used for encryption and digital signatures.
rsh	Remote Shell – an older Unix command and protocol used to execute commands on remote systems. It has largely been replaced by SSH.
RSS	Really Simple Syndication – a family of XML-based formats used to publish frequently updated content such as news, articles, blog posts and podcasts.
RSS Feed	A structured document, commonly using RSS or Atom, containing a list of recently published or updated content from a website or other service.
RSTP	Rapid Spanning Tree Protocol – an enhanced version of Spanning Tree Protocol designed to achieve faster convergence after topology changes.
rsync	A utility and protocol for efficiently synchronising files and directories between locations by transferring only data that needs to be updated.
rsync daemon	A background service providing rsync file synchronisation over a network without requiring an interactive login.
rsyslog	A widely used Unix/Linux logging system supporting syslog protocols and additional features such as filtering, forwarding and structured processing
RTC	Real-Time Clock – a clock circuit that maintains time independently of the main processor and normally continues operating while the computer is powered off using a small battery or other power source.
RTFM	Read The Fine Manual – a humorous expression suggesting that the answer to a technical question can be found in the relevant documentation.
RTOS	Real-Time Operating System – an operating system designed to provide predictable response times and scheduling behaviour for time-sensitive applications.
RTS	Request To Send – a control signal or protocol mechanism used in communications to indicate that a device wishes to transmit data.
RTSP	Real Time Streaming Protocol – a network control protocol commonly used to establish and control streaming media sessions, including network camera video streams.
run-time	The period during which a program is executing.
runlevel	A traditional Unix and Linux concept representing a particular system operating state and associated collection of services. Modern systemd systems generally use targets instead.
runpath	A dynamic-linking path stored in an executable or shared object and used by the loader when searching for required libraries.
runtime	The period during which a program is executing, or the software environment and supporting components required for a program to execute.
runtime error	An error detected while a program is executing rather than during compilation or static analysis.
runtime library	A library providing functions and support required by programs during execution, often supplied by the programming language or operating system environment.
salt	Random or unique data added to a password or other input before hashing, making precomputed hash attacks more difficult.
Samba	Free and open-source software implementing the Server Message Block protocol, allowing Unix-like systems to provide and access Windows-compatible file and printer sharing.
same-origin policy	A browser security rule restricting scripts and other web content from freely interacting with resources belonging to different origins.
Sandbox	An isolated environment in which software can run with restricted access to the host system or other resources.
sandbox escape	A security failure in which software running inside an isolated environment gains access to resources or privileges outside the intended boundary.
SAS	Serial Attached SCSI – a serial storage interface used particularly in servers and enterprise storage systems.
SATA	Serial ATA – an interface commonly used to connect storage devices such as hard disk drives and SATA SSDs to computers.
SBC	Single-Board Computer – a complete computer built on a single circuit board, typically including processor, memory, storage interfaces and peripheral connections.
SBOM	Software Bill of Materials – a structured inventory identifying the software components and dependencies contained in a product or application.
scheduler	An operating-system component responsible for deciding which runnable process or thread should receive processor time.
scheduling quantum	A period of processor time allocated to a process or thread before the scheduler may switch execution to another runnable task.
scope	The region of a program within which a name, variable or other declaration is accessible.
scp	Secure Copy Protocol – a method of securely copying files between computers using the Secure Shell infrastructure.
screen	GNU Screen – a terminal multiplexer allowing multiple interactive shells and programs to run within one terminal session.
scrypt	A password-based key derivation function designed to make large amounts of memory necessary for efficient password guessing.
SCSI	Small Computer System Interface – a family of standards for connecting and communicating with storage devices and other peripherals.
SD card	A removable flash-memory storage card conforming to the Secure Digital storage standard.
SDK	Software Development Kit – a collection of tools, libraries, documentation and other resources used to develop software for a particular platform or technology.
SDR	Standard Dynamic Range – conventional image or video representation with a more limited luminance range than HDR.
seccomp	Secure Computing – a Linux kernel facility allowing a process to restrict the system calls it may make.
Secondary Storage	Non-volatile storage used to retain data and programs when a computer is powered off, such as SSDs and hard disk drives.
sector	A logical or physical subdivision of a storage device used as a basic unit of addressing or data transfer.
secure boot	A boot mechanism using cryptographic verification to ensure that only trusted boot software and operating-system components are executed.
security patch	A software update intended specifically to correct one or more security vulnerabilities.
sed	Stream Editor – a Unix and Linux command-line utility used to perform operations such as searching, filtering and replacing text in input streams or files.
Seed	A participant in a BitTorrent swarm that possesses a complete copy of the content being distributed and can upload pieces to other participants.
Seeding	The process of uploading data to other BitTorrent participants after obtaining some or all of the content.
segfault	Informal name for a segmentation fault, in which a program attempts an invalid memory access and the operating system terminates it.
segmentation fault	An error occurring when a program attempts to access memory in a manner that the operating system does not permit, commonly causing the program to terminate.
SELinux	Security-Enhanced Linux – a Linux security framework implementing mandatory access controls using security policies and labels.
semantic	Relating to the meaning or behaviour represented by a program statement, expression or data rather than its syntactic form.
semantic diff	A comparison that attempts to identify meaningful structural or logical changes rather than merely textual differences.
semantic versioning	A version-numbering convention using MAJOR.MINOR.PATCH components to communicate the significance of software changes.
semantics	The meaning and behaviour associated with valid statements, expressions or constructs in a programming language or other formal system.
semaphore	A synchronisation mechanism using a counter or state to control access to shared resources by concurrent processes or threads.
SemVer	Semantic Versioning – a convention for assigning software version numbers according to the nature of changes between releases.
sequential consistency	A memory-consistency model in which the observable result of concurrent operations is consistent with some single sequential ordering of those operations.
Server	A computer or software system that provides services, resources or data to other computers or programs called clients.
Service	A background software component that performs a specific function or provides functionality to other programs or users.
Service Account	A user account created for use by a computer service, application or automated process rather than a human user.
service discovery	The process of identifying network services, endpoints or resources available on a host or network.
Session	A period of interaction between a user or client and a computer service, commonly maintained using authentication information or a session identifier.
session cookie	A web cookie normally associated with a browser session and not intended to persist after the browsing session ends.
session ID	An identifier associated with a Unix process session.
session leader	A Unix process that has created a new session and whose process ID is equal to the session ID.
setgid	A Unix file permission mechanism that can cause an executable to run with the effective group identity of the file owner, and on directories can cause new files to inherit the directory group.
setuid	A Unix file permission mechanism causing an executable program to run with the effective user identity of the file owner.
SFP	Small Form-factor Pluggable – a compact, replaceable network transceiver commonly used in Ethernet switches and other networking equipment.
SFP+	An enhanced Small Form-factor Pluggable transceiver form factor commonly used for higher-speed Ethernet connections such as 10 Gigabit Ethernet.
sftp	SSH File Transfer Protocol – a file-transfer protocol operating over a secure SSH connection.
SHA-1	Secure Hash Algorithm 1 – a 160-bit cryptographic hash function. SHA-1 is no longer considered suitable for security-sensitive collision-resistant applications.
SHA-2	A family of cryptographic hash functions including SHA-224, SHA-256, SHA-384 and SHA-512.
SHA-256	Secure Hash Algorithm 256-bit – a cryptographic hash function producing a 256-bit digest and widely used for integrity checking and security applications.
Shadow Banning	A moderation or visibility-limiting practice in which an account or its content is made less visible to other users without the account holder necessarily being explicitly informed.
Share (social media)	An action that distributes or republishes content to other users, accounts, communities, or communication channels.
shared library	A library of compiled code that can be loaded by multiple programs at run time rather than being copied separately into each executable.
shared memory	A region of memory mapped into multiple processes so that they can exchange data directly.
shared memory IPC	Inter-process communication using a region of memory mapped into multiple processes.
shared object	A compiled library or other binary component designed to be loaded dynamically by programs, commonly using the .so filename extension on Unix-like systems.
shebang	The character sequence #! at the beginning of an executable script, followed by the path to an interpreter that should be used to execute the script.
Shell	A program that provides an interface through which a user or another program can interact with an operating system.
shell builtin	A command implemented directly by a shell rather than as a separate executable program, such as cd or export in many Unix shells.
shell expansion	The processing performed by a shell to expand variables, wildcards, command substitutions and other expressions before executing a command.
shell function	A named shell construct containing commands that can be invoked as a unit within the shell.
shell prompt	The text or graphical indicator displayed by a command shell to show that it is ready to accept another command.
Shell Script	A text file containing commands and programming constructs intended to be executed by a command-line shell.
shutdown	The process of stopping an operating system and normally powering off or otherwise halting the computer.
SID	Session ID – the identifier associated with a Unix process session.
side effect	A change caused by evaluating or executing an operation beyond simply producing its return value, such as modifying state or performing I/O.
SIGABRT	Abort signal – a Unix/Linux signal normally generated when a process calls abort() or encounters certain fatal internal errors.
SIGCHLD	A Unix signal sent to a parent process when one of its child processes terminates, stops or resumes under conditions defined by the operating system.
SIGCONT	A Unix signal requesting that a stopped process resume execution.
SIGHUP	Signal Hang Up – a Unix and Linux signal originally associated with a terminal connection being disconnected and commonly used to request that a daemon reload its configuration.
SIGINT	Signal Interrupt – a Unix and Linux signal normally generated by pressing Ctrl-C in a terminal to request interruption of the foreground process.
SIGKILL	Signal Kill – a Unix and Linux signal that immediately terminates a process and cannot be caught, blocked or ignored by the target process.
signal	A Unix and Linux mechanism used to notify a process that an event has occurred or that it should perform a particular action.
signal handler	A function or routine executed by a program in response to a Unix signal.
signal mask	A per-thread set of Unix signals that are currently blocked from normal delivery.
SIGPIPE	A Unix signal generated when a process writes to a pipe or socket whose reading end has been closed.
SIGSEGV	Segmentation Violation – the Unix/Linux signal normally delivered when a process performs an invalid memory access.
SIGSTOP	A Unix signal that forcibly stops a process. Unlike SIGTSTP, it cannot be caught, blocked or ignored by the target process.
SIGTERM	Signal Terminate – a Unix and Linux signal requesting that a process terminate, allowing the program an opportunity to perform cleanup.
SIGUSR1	User-defined Unix signal 1, available for application-specific purposes.
SIGUSR2	User-defined Unix signal 2, available for application-specific purposes.
single-user mode	A restricted Unix or Linux operating state intended primarily for system maintenance, traditionally providing a single administrative session with many normal services stopped.
sitemap	A structured listing of URLs belonging to a website, commonly provided to search engines to help them discover and index site content.
SLA	Service Level Agreement – a formal agreement defining expected levels of service, availability, response times or other measurable commitments.
sleep	A general term for a low-power computer state in which normal execution is suspended until the system is awakened.
SLIP	Serial Line Internet Protocol – an early protocol for transmitting IP packets over serial connections, later largely superseded by PPP.
SMART	Self-Monitoring, Analysis and Reporting Technology – a monitoring system implemented by many storage devices to report information about their condition and potentially indicate developing faults.
SMB	Server Message Block – a network protocol used for file, printer and other resource sharing, particularly in Microsoft Windows environments.
SMB share	A file or printer resource made available over a network using the Server Message Block protocol.
SMP	Symmetric Multiprocessing – a computer architecture in which multiple processors or CPU cores have broadly equal access to shared system memory.
SMT	Simultaneous Multithreading – a processor technique allowing multiple hardware threads to issue instructions using a single physical CPU core.
SMTP	Simple Mail Transfer Protocol – the standard protocol commonly used to send email between mail clients and servers and between mail servers.
SMTP Relay	A mail server function that accepts an email message and forwards it towards another mail server for delivery.
Snapshot	A point-in-time representation of data, a filesystem or a virtual machine that can be used for recovery, testing or backup purposes.
SNMP	Simple Network Management Protocol – a protocol used to monitor and manage network devices and systems.
SO file	A shared-object file containing compiled code or data that can be loaded dynamically by programs on Unix-like systems.
SOA record	Start Of Authority – a DNS record containing administrative information about a DNS zone, including its primary name server and serial number.
SoC	System on Chip – an integrated circuit combining major computer components such as CPU cores, memory controllers and peripheral interfaces on one chip.
Social Graph	A representation of the relationships and connections between users, accounts, groups, and other entities within an online social network.
Social Media	Internet-based services that allow users to create, publish, share, discover, and interact with content and with other users or communities.
Social Network	An online service or system in which users create accounts and establish relationships or connections with other users.
Social Platform	An online service that provides facilities for users or organisations to publish content, communicate, interact, or participate in communities.
Socket	A software endpoint used by applications to communicate over a network, typically identified by an IP address and port together with a transport protocol.
socket pair	A pair of connected communication endpoints, commonly used to describe the two endpoints participating in a network or local socket connection.
Soft Link	Another name for a symbolic link, a filesystem object that references another file or directory.
soft real-time	A real-time system in which occasional missed timing deadlines are undesirable but generally do not cause catastrophic failure.
soft reset	A reset initiated through software or normal system mechanisms that allows at least some controlled shutdown or restart processing.
Software	Programs, instructions and associated data that tell a computer how to perform tasks.
SOLID	A group of five object-oriented software-design principles concerning responsibility, extensibility, substitutability, interface design and dependency management.
soname	A shared-library identifier used by Unix/Linux dynamic linking mechanisms to identify the compatible library interface required by an executable.
sort	A Unix and Linux command that reads lines of text and outputs them in sorted order.
Source Code	Human-readable program instructions written in a programming language before being compiled or otherwise transformed into executable code.
source compatibility	The ability of existing source code to continue compiling against a newer version of a library, compiler or interface.
source distribution	A software distribution containing source code intended to be compiled or otherwise processed by the recipient.
source package	A software package containing source code and associated build metadata from which binary packages can be produced.
source tarball	A compressed archive containing the source code of a software project, commonly distributed as a release package.
Spam	Unsolicited bulk electronic messages, particularly unwanted email, but also including unwanted messages distributed through other communication systems.
Spam Account	An account used primarily to distribute unsolicited, repetitive, deceptive, promotional, or otherwise unwanted content or interactions.
Spambot	An automated program used to generate, distribute or collect information for unsolicited bulk messaging.
span	A timed unit of work within a distributed trace, representing an operation performed by a service or component.
sparse file	A file whose logical size is larger than the amount of physical storage allocated because regions containing only zeros are represented without allocating corresponding disk blocks.
speculative execution	A processor technique in which instructions are executed before it is certain that their results will be needed, with incorrect speculative work later discarded.
SPF	Sender Policy Framework – an email authentication mechanism allowing a domain to specify which mail servers are authorised to send messages using that domain.
SPI	Serial Peripheral Interface – a synchronous serial communication interface commonly used to connect processors and embedded peripherals.
spider	Another name for a web crawler, particularly one used by a search engine to discover and retrieve web pages.
spinlock	A synchronisation mechanism in which a thread repeatedly checks a lock until it becomes available rather than immediately sleeping.
split DNS	A DNS configuration in which different answers are provided for the same domain name depending on where the query originates, commonly giving internal clients different results from external clients.
SQL	Structured Query Language – a language commonly used to create, query, modify and manage data in relational databases.
SQL Injection	A security vulnerability in which malicious SQL syntax is inserted into application input and subsequently interpreted as part of a database query.
SSD	Solid State Drive – a storage device that uses flash memory rather than spinning magnetic disks to store data.
ssh	Secure Shell – a protocol providing encrypted remote login, command execution and other secure services over a network.
SSH agent	A program that holds private SSH authentication keys in memory and performs cryptographic authentication operations on behalf of SSH clients.
SSH Key	A cryptographic key used with Secure Shell to authenticate a user or system, commonly using a public/private key pair.
SSID	Service Set Identifier – the name normally displayed to users for a Wi-Fi network.
SSID broadcast	The transmission of Wi-Fi network-identification information by an access point so that compatible clients can discover the network.
SSL	Secure Sockets Layer – an older cryptographic protocol that preceded TLS and is now considered obsolete. The term is still commonly used informally when referring to TLS-secured connections.
stable release	A software release intended for general use after development and testing have reached a level considered suitable for production.
stack	A memory area or abstract data structure commonly used for function call state, local variables and temporary values.
stack canary	A value placed near sensitive stack data so that a stack-buffer overflow can be detected before corrupted control information is used.
stack overflow	A condition in which a program exhausts the available stack space, commonly caused by excessive recursion or very large automatic allocations.
stack pointer	A CPU register containing the address associated with the current top of the program stack.
stack trace	A record showing the sequence of active function calls leading to a particular point in program execution, commonly used when diagnosing errors or crashes.
staging area	In Git, the intermediate area containing changes selected for inclusion in the next commit.
standard library	A collection of commonly required functions, classes or other facilities provided as part of a programming language or development environment.
standard streams	The conventional input and output channels provided to Unix and Linux processes: standard input, standard output and standard error.
starvation	A condition in which a process or thread is repeatedly denied the resources or CPU time it needs to make progress.
stateful firewall	A firewall that tracks the state of network connections and uses that information when deciding whether traffic should be allowed.
stateless firewall	A firewall that evaluates network packets independently without maintaining connection state.
statement	A complete instruction or operation in a programming language.
static analysis	The automated examination of source code or compiled code without executing the program in its normal operating environment.
Static IP	An IP address configured to remain fixed rather than being automatically assigned dynamically by a service such as DHCP.
static library	A library of compiled code incorporated into a program during the linking stage rather than being loaded separately at run time.
Static Linking	A software linking method in which required library code is incorporated into an executable during the build process.
static typing	A programming-language system in which types are determined or checked before program execution, commonly during compilation.
stderr	Standard Error – the conventional output stream used by Unix and Linux programs for diagnostic and error messages.
stdin	Standard Input – the conventional input stream of a Unix or Linux process, normally connected to the controlling terminal unless redirected.
stdout	Standard Output – the conventional output stream of a Unix or Linux process, normally displayed on the terminal unless redirected.
sticky bit	A Unix filesystem permission bit with special behaviour on directories, commonly preventing users from deleting or renaming files owned by other users in shared directories such as /tmp.
sticky directory	A directory with the sticky permission bit set, restricting deletion or renaming of entries to their owners, the directory owner or an appropriately privileged user.
STL	STereoLithography – a file format widely used for representing the surface geometry of three-dimensional objects, particularly in 3D printing and computer-aided manufacturing.
Storage Pool	A collection of physical storage resources managed together and presented as a combined pool from which logical storage can be allocated.
Story (social media)	A temporary social-media post or sequence of posts that is normally designed to disappear or become unavailable after a limited period.
STP	Shielded Twisted Pair – twisted-pair network cabling incorporating shielding intended to reduce electromagnetic interference.
strace	A Unix and Linux diagnostic utility that traces system calls and signals made by a process.
stress test	A test designed to place sustained or unusually high loads on a system or component to evaluate performance, stability or reliability.
strings	A Unix/Linux utility that extracts sequences of printable characters from binary or other files.
strip	A Unix/Linux utility that removes symbol and debugging information from object files and executables, often reducing their size.
stripped binary	An executable or object file from which unnecessary symbol and debugging information has been removed, reducing its size.
strong typing	A property of a programming language in which operations between incompatible data types are restricted or require explicit conversion.
struct	A programming-language construct used to group multiple related values, potentially of different data types, into one composite data type.
structure	A composite data type or organised arrangement of related data elements.
stub	A simplified replacement for a software component, commonly used during testing to provide predefined behaviour.
STUN	Session Traversal Utilities for NAT – a protocol allowing a device to discover its public-facing address and port as seen from outside a NAT device.
su	Substitute User – a Unix and Linux command used to switch to another user account, commonly root.
subdomain	A DNS domain located beneath another domain in the hierarchical naming system, such as mail.example.org beneath example.org.
Subnet	A logically divided portion of an IP network. Subnetting allows a larger network to be divided into smaller networks.
Subnet Mask	A value used with an IPv4 address to identify which portion represents the network and which portion represents the host.
Subnetting	The process of dividing an IP network into smaller logical networks called subnets.
Subpixel	An individual red, green or blue component within a pixel on a display, or the smallest independently controlled colour component used to produce the appearance of a full-colour pixel.
subshell	A child shell process created to execute commands in a separate shell environment.
sudo	Superuser DO – a Unix and Linux facility allowing authorised users to execute commands with the privileges of another user, commonly the root account.
sudoers	The configuration defining which users or groups are permitted to execute particular commands using sudo and under which conditions.
superblock	Filesystem metadata describing fundamental characteristics of a filesystem, such as its size, block structure and state.
superuser	A user account with elevated privileges that can perform administrative operations normally restricted from ordinary users. On Unix and Linux systems this is commonly the root account.
supply-chain attack	An attack in which an attacker compromises software, hardware, dependencies or distribution infrastructure so that malicious content reaches otherwise trusted users.
SUS	Single UNIX Specification – a family of standards defining interfaces and behaviour for Unix systems and applications.
suspend	A power-management state in which system activity is paused and much of the hardware is placed into a low-power state while memory contents are retained.
SVG	Scalable Vector Graphics – an XML-based format for representing two-dimensional vector graphics that can be scaled without the loss of quality associated with raster images.
Swap	Storage space used by an operating system as an extension of RAM when physical memory is under pressure.
Swap File	A file on storage that an operating system can use as virtual memory when physical RAM is insufficient.
swap space	Storage space used by an operating system to hold memory pages that have been moved out of physical RAM.
swapfile	A regular file configured by a Unix or Linux operating system for use as swap space.
swappiness	A Linux kernel parameter influencing how readily the operating system moves memory pages between physical RAM and swap space.
swapping	The process of moving memory pages between physical RAM and secondary storage to manage limited physical memory.
Swarm	The collection of peers participating in the distribution of a particular file or set of data using BitTorrent.
SWD	Serial Wire Debug – a two-wire ARM debugging interface used for programming and debugging compatible microcontrollers.
switch	A network device that forwards Ethernet frames between connected devices, normally using MAC addresses to determine the appropriate port.
symbol	A named identifier representing a function, variable or other entity in compiled or linked software.
symbol resolution	The process by which a linker or loader associates references to symbols with their actual definitions.
symbol table	A data structure in an object file or executable containing information about symbols and their associated addresses or other attributes.
Symbolic Link	A filesystem object that contains a reference to another file or directory, commonly used on Unix-like systems.
symbolic resolution	The process by which a linker or dynamic loader determines which definition satisfies a reference to a symbol.
symlink	A symbolic link – a filesystem object containing a pathname that refers to another file or directory.
symmetric encryption	Encryption in which the same secret key, or closely related secret keys, is used for encryption and decryption.
sync	An operation or command requesting that pending filesystem data and metadata be written out to storage.
synchronisation	Mechanisms used to coordinate concurrent processes or threads and control access to shared resources.
synchronous I/O	Input/output operations in which the calling operation normally waits until the requested I/O has completed or reached an appropriate state.
syntax	The set of rules defining how valid expressions, statements or other constructs must be written in a programming language or data format.
Sysadmin	System Administrator – a person responsible for installing, configuring, maintaining and troubleshooting computer systems and related services.
syscall	A request made by a user-space program to the operating-system kernel to perform a privileged or kernel-managed operation.
sysctl	A Unix and Linux interface and command used to view or change kernel parameters while the system is running.
sysctl.conf	A configuration file commonly used on Linux systems to define kernel parameters that should be applied through sysctl.
sysfs	A virtual Linux filesystem exposing information about devices, drivers, kernel objects and hardware topology, normally mounted at /sys.
Syslog	A standardised system for generating, transmitting and storing log messages from computer systems and network devices.
syslog-ng	An open-source logging system implementing syslog-style message collection, filtering, routing and storage.
Sysop	System Operator – a person responsible for operating and administering a computer system or online service, particularly a Bulletin Board System.
sysroot	A directory tree used by a compiler and linker as an alternative root filesystem containing headers, libraries and other files for a target system.
System Call	A controlled request made by a program to an operating system kernel to perform a privileged or system-level operation.
system call interface	The interface through which user-space programs request services from an operating-system kernel.
system clock	The clock maintained and used by an operating system to provide the current time to applications and system services.
Systemd	A widely used Linux system and service manager responsible for starting services and managing various system resources.
systemd target	A systemd unit used to group other units and represent a particular system state or collection of services.
systemd unit	A configuration object managed by systemd representing a resource such as a service, socket, mount point, device, timer or target.
tag	A named identifier attached to a particular version or point in a software repository, commonly used to mark releases.
Tag (social media)	A reference that associates a user, account, object, or other entity with a piece of online content, often causing the associated account to receive a notification.
tail	A Unix and Linux command that displays the end of a file or stream. It is commonly used with the -f option to monitor a growing log file.
tar	A Unix utility and archive format commonly used to combine multiple files and directories into a single archive.
tarball	An archive file, commonly created using tar and often compressed, containing a collection of files distributed as a single package.
target	In a build system such as make, a named output or action that can be produced or performed according to a set of rules.
target architecture	The processor architecture for which software is being compiled or otherwise prepared to run.
TCP	Transmission Control Protocol – a connection-oriented Internet protocol that provides reliable, ordered delivery of data between applications.
TCP/IP	Transmission Control Protocol/Internet Protocol – the family of networking protocols that forms the foundation of the Internet and many other computer networks.
TDP	Thermal Design Power – a design parameter representing the approximate amount of heat a cooling system is expected to dissipate from a processor or other component under specified conditions.
technical debt	The future cost created by choosing a quick or imperfect technical solution instead of a more robust solution, often increasing the effort required for later maintenance.
tee	A Unix and Linux command that reads standard input and writes it both to standard output and to one or more files.
telemetry	Automatically collected measurements or events describing the operation or behaviour of a system or application.
Telnet	An Internet protocol and command-line client historically used for interactive remote login and communication with network services. It provides no encryption and is generally unsuitable for secure remote administration.
temporary file	A file created for short-term storage of intermediate or transient data and normally intended to be removed after use.
Terminal	A text-based interface through which a user can interact with a computer, commonly by entering commands into a shell.
terminal driver	Operating-system code responsible for managing communication between terminal devices and user processes.
terminal emulator	Software that provides a graphical or other interface behaving like a computer terminal, allowing users to interact with a command shell or other terminal-based program.
terminal multiplexer	Software allowing multiple terminal sessions or programs to run within a single terminal connection, commonly allowing sessions to survive disconnection.
test harness	Software and supporting infrastructure used to execute tests and collect or evaluate their results.
TFTP	Trivial File Transfer Protocol – a very simple file-transfer protocol commonly used for tasks such as network booting and transferring firmware to network devices.
thermal paste	A thermally conductive compound placed between a heat-producing component and its heatsink to improve heat transfer by filling microscopic surface gaps.
thermal runaway	A condition in which increasing temperature causes further heat generation or degradation, potentially leading to hardware failure if not controlled.
thermal throttling	The automatic reduction of processor or other hardware performance to reduce heat generation when a temperature limit is approached.
thin provisioning	A storage technique in which logical storage capacity can be allocated without immediately reserving the corresponding physical storage.
thrashing	A condition in which a system spends excessive time moving memory pages between RAM and backing storage instead of performing useful work.
Thread	A sequence of instructions within a process that can be scheduled for execution independently of other threads in the same process.
Thread (social media)	A sequence of connected posts or messages from one or more users forming a continuing conversation or extended piece of content.
Thread Safety	The property of software code that allows it to operate correctly when accessed or executed concurrently by multiple threads.
thread-local storage	Storage providing each thread with its own independent instance of a variable or data area.
thread-safe	Describing software that can safely be executed concurrently by multiple threads without causing incorrect results or corruption.
threat model	A structured description of potential attackers, assets, attack methods and security assumptions relevant to a system.
three-way merge	A merge technique comparing two changed versions with their common ancestor to determine how the changes should be combined.
throttling	Deliberately limiting the rate at which a system performs or accepts operations, often to protect resources or control network traffic.
Throughput	The amount of data successfully processed or transferred during a given period of time.
Throughput Limit	A configured maximum rate at which a system, connection or application is permitted to process or transfer data.
thumbnail	A reduced-size representation of an image or other media, commonly used for previews and galleries.
TIFF	Tagged Image File Format – a flexible image file format widely used for high-quality photographs, scanning, publishing and professional image processing.
tilde expansion	A shell feature that expands the tilde character to a user's home directory or related directory locations.
Time Server	A computer or service that provides accurate time information to other systems, commonly using NTP.
time slice	A period of processor time allocated to a process or thread by a scheduler before another task may be selected.
Timeline (social media)	A chronological or algorithmically ordered stream of posts, updates, or other activity presented to a user.
timer unit	A systemd unit that schedules another unit to be activated at a specified time or according to a defined interval.
timezone	A geographical or administrative region with defined rules for its local civil time, including changes such as daylight saving time where applicable.
TLB	Translation Lookaside Buffer – a processor cache storing recent virtual-to-physical address translations to speed up memory access.
TLD	Top-Level Domain – the highest level of the Domain Name System hierarchy, such as .org, .uk or .com.
TLS	Transport Layer Security – a cryptographic protocol used to provide secure communication over networks, including encrypted web connections.
TLS Certificate	A digital certificate used to authenticate a server or other endpoint and establish encrypted communications using TLS.
TLS Handshake	The initial negotiation process used by TLS endpoints to establish cryptographic parameters and authenticate identities before protected data is exchanged.
tmpfs	Temporary File System – a filesystem whose contents are normally stored in volatile memory and which is commonly used for temporary data on Unix and Linux systems.
tmux	A terminal multiplexer commonly used on Unix and Linux systems to maintain multiple shell sessions within a single terminal and to allow sessions to persist after disconnecting.
Token	A piece of data representing a value, permission, session, authentication state or other information used by a software system.
toolchain	A collection of development tools used together to build software, commonly including a compiler, assembler, linker and debugger.
top	A Unix and Linux interactive command-line utility displaying running processes and system resource usage such as CPU and memory consumption.
Tor	The Onion Router – a network and software system designed to provide privacy by routing communications through multiple relays and obscuring the source of connections.
torrent	A file or metadata structure used by BitTorrent to describe content and provide information needed to participate in distributing it.
Torrent File	A small file containing metadata describing content distributed through BitTorrent, including information needed by a BitTorrent client to locate and exchange pieces of the content.
TOTP	Time-based One-Time Password – an authentication mechanism generating temporary numeric codes based on a shared secret and the current time.
touch	A Unix and Linux command used to update file timestamps and, if a specified file does not exist, create an empty file.
TPM	Trusted Platform Module – a hardware security component providing facilities such as protected key storage, cryptographic operations and platform integrity measurements.
tr	Translate – a Unix and Linux command used to translate, delete or compress characters in input text.
trace ID	An identifier used to associate related operations belonging to the same distributed trace.
trace logging	Very detailed logging intended to record fine-grained program execution or diagnostic information.
tracepath	A Linux network diagnostic utility similar to traceroute that can also detect path maximum transmission unit information.
traceroute	A network diagnostic utility that determines the sequence of routers or network hops through which packets travel towards a destination.
tracker	In BitTorrent, a server that helps participating clients discover other peers sharing the same content. More generally, the term can describe software that records or monitors activity.
Transaction	A logical unit of database operations that is treated as a single operation, commonly providing properties such as atomicity, consistency, isolation and durability.
Transistor	A semiconductor device used to amplify or switch electronic signals and forming a fundamental building block of modern computer processors and memory.
Transit Provider	A network operator that provides connectivity allowing traffic from one network to reach other networks and destinations across the Internet.
transitive dependency	A dependency required indirectly because it is itself required by another dependency.
trap	A shell facility allowing a script to specify commands to execute when particular signals or shell events occur.
tree	A command-line utility that displays files and directories in a hierarchical tree-like format.
Trending	Describing content, subjects, phrases, or topics that are experiencing unusually high levels of attention or discussion within an online service.
Trending Topic	A subject, phrase, hashtag, or other topic that is currently receiving a high level of discussion or attention within an online service.
TRIM	A storage command allowing an operating system to inform an SSD which blocks of data are no longer required, helping the device manage flash storage efficiently.
Trojan	Malicious software that disguises itself as legitimate software or files in order to trick a user into running it.
Troll	A person or account that deliberately provokes, antagonises, or disrupts other users, often to generate emotional reactions or conflict.
Trolling	The deliberate use of provocative, antagonistic, disruptive, or inflammatory behaviour online to provoke reactions or disturb a discussion or community.
trunk port	A switch port configured to carry traffic belonging to multiple VLANs, normally using IEEE 802.1Q tagging.
TTL	Time To Live – a value specifying how long information may be cached or how many network hops a packet may traverse, depending on the protocol in which it appears.
tty	Teletypewriter – a Unix and Linux term referring to a terminal device. The name originates from physical teleprinter terminals used with early computer systems.
tune2fs	A Linux utility for adjusting filesystem parameters and displaying information about ext2, ext3 and ext4 filesystems.
tunnel	A mechanism for carrying one type of network traffic inside another protocol or connection, commonly used for VPNs and other network links.
Tunnelling	The process of encapsulating one type of network traffic within another protocol or connection so that it can travel across a network.
TURN	Traversal Using Relays around NAT – a protocol allowing real-time communications traffic to be relayed through a server when direct peer-to-peer communication is not possible.
Two-Factor Authentication	An authentication method requiring two different types of evidence, such as a password and a code generated by a separate device.
TXT Record	A DNS record containing arbitrary text information, commonly used for verification and email-security mechanisms such as SPF and domain ownership checks.
type casting	The explicit conversion of a value from one data type to another.
type checking	The process of determining whether values and operations are used with compatible data types according to the rules of a programming language.
type inference	The process by which a programming language or compiler determines the type of an expression or variable from its context without requiring the type to be written explicitly.
typosquatting	The registration or use of names deliberately resembling legitimate domain names, package names or identifiers in order to exploit typing errors or visual similarity.
UART	Universal Asynchronous Receiver-Transmitter – hardware implementing asynchronous serial communication, commonly used for console access and communication between embedded devices.
udev	The Linux device manager responsible for dynamically managing device nodes and handling device events as hardware is detected or removed.
udev rule	A rule used by the Linux udev device manager to specify how particular devices should be handled or named.
udevadm	A command-line utility used to query and control the Linux udev device manager.
UDF	Universal Disk Format – a filesystem specification commonly used for optical media and some removable storage applications.
UDP	User Datagram Protocol – a connectionless network protocol that sends datagrams without guaranteeing delivery, ordering or duplicate protection.
UDP Port	A numbered endpoint used by UDP to identify a particular application or service receiving network datagrams.
UEFI	Unified Extensible Firmware Interface – a modern firmware interface that replaces or extends many traditional BIOS functions and provides a standard environment for starting an operating system.
UEFI application	A program designed to run directly from UEFI firmware before an operating system is loaded.
UGC	An abbreviation for user-generated content, meaning digital content created and published by users of an online service.
UID	User IDentifier – a numerical identifier assigned to a user account by a Unix or Linux operating system.
ulimit	A shell facility and system interface used to display or configure resource limits imposed on processes, such as maximum open files or core-dump size.
umask	User file-creation mode mask – a value used by Unix and Linux systems to determine which permission bits are cleared when new files and directories are created.
uname	Unix Name – a Unix and Linux command that reports information about the operating system and kernel.
undefined behaviour	Program behaviour for which a language specification imposes no requirements, meaning the implementation is not required to produce any particular result.
Unicast	A networking method in which data is sent from one sender to one specific destination.
Unicode	A universal character set and associated standards defining code points and representations for text used across computing systems.
unified diff	A standard textual representation of changes showing added and removed lines together with contextual information.
union filesystem	A filesystem mechanism presenting multiple underlying directories or filesystems as a single combined hierarchy.
uniq	A Unix and Linux command that reports or removes adjacent repeated lines from sorted or otherwise appropriately ordered input.
unit test	An automated test designed to verify the behaviour of a small, relatively isolated component of software.
Unix	A family of operating systems and related standards originating from the original Unix operating system developed at Bell Labs.
Unix certification	Formal certification that an operating system conforms to the requirements of the Single UNIX Specification. Not all Unix-like operating systems are certified.
Unix domain socket	A socket providing inter-process communication between processes on the same Unix/Linux system, using the filesystem namespace or an abstract namespace rather than an IP network.
Unix epoch	The reference instant 1970-01-01 00:00:00 UTC from which Unix timestamps are conventionally measured.
Unix philosophy	A set of design principles associated with Unix, commonly emphasising small tools that perform focused tasks and can be combined through standard interfaces such as pipes.
Unix timestamp	A numerical representation of a point in time based on the Unix epoch, conventionally expressed as the number of seconds elapsed since 1970-01-01 00:00:00 UTC.
Unix-like	Describing an operating system that follows significant design principles, interfaces or behaviours associated with Unix without necessarily being derived from the original Unix source code.
unmount	The process of detaching a mounted filesystem from the filesystem hierarchy.
unresolved symbol	A reference to a function, variable or other symbol for which no corresponding definition has yet been found during linking or loading.
Upload	The process of transferring data from a local computer or device to a remote computer or server.
upstream	In software development, the original project or source from which a distribution or downstream project obtains code or changes.
upstream patch	A software patch submitted to or originating from the original project rather than being maintained only by a downstream distributor.
upstream server	A server to which another server forwards requests, commonly used when describing reverse proxies, gateways or application servers.
uptime	The amount of time a computer or service has been running continuously since it was last started or restarted.
uptime SLA	A service-level commitment specifying a target percentage of time during which a service is expected to remain available.
URI	Uniform Resource Identifier – a general identifier for a resource, of which a URL is a commonly used form.
URL	Uniform Resource Locator – an address that identifies the location of a resource on a network, commonly a web page or other Internet resource.
URN	Uniform Resource Name – a URI intended to provide a persistent, location-independent name for a resource.
USB	Universal Serial Bus – a standard for connecting computers to peripherals and other devices and for transferring data and electrical power.
USB HID	USB Human Interface Device – a USB device class commonly used by keyboards, mice, game controllers and similar input devices.
USB hub	A device allowing multiple USB devices to share one USB host connection.
USB Mass Storage	A USB device class allowing storage devices such as flash drives and external disks to communicate with computers using standardised mass-storage protocols.
USB-C	A reversible USB connector standard used for data transfer, charging and, depending on the implementation, display and other functions.
use-after-free	A programming error in which software accesses memory after it has been released, potentially causing crashes, data corruption or security vulnerabilities.
Usenet	A distributed Internet discussion system in which messages are organised into newsgroups and exchanged between servers using NNTP. It predates the World Wide Web and remains accessible today.
Usenet Feed	A stream of Usenet messages exchanged between news servers, normally using NNTP.
Usenet Killfile	A feature of a Usenet newsreader that automatically hides messages or threads matching specified criteria, such as particular authors or subjects.
Usenet Thread	A sequence of related Usenet messages consisting of an original article and its replies and follow-up discussions.
User Account	An identity maintained by an operating system or service that allows an individual or program to be authenticated and assigned permissions.
user agent	A software component that communicates using a network protocol on behalf of a user or another application. In HTTP, the User-Agent header commonly identifies the client software.
user mode	The processor execution mode in which ordinary application code executes with restricted privileges.
user namespace	A Linux namespace allowing a process to have different user and group ID mappings from those of the surrounding system.
User Space	The area of memory and execution environment in which normal application programs operate outside the privileged operating-system kernel.
User-Generated Content	Digital content created and published by users rather than solely by the operator or owner of an online service.
UTC	Coordinated Universal Time – the international time standard used as the basis for civil timekeeping worldwide and commonly used by computers, servers, networks and scientific systems.
UTF-16	A Unicode character encoding using one or two 16-bit code units to represent characters.
UTF-32	A Unicode encoding that represents each Unicode code point using 32 bits. It is simple but generally less storage-efficient than UTF-8 or UTF-16.
UTF-8	Unicode Transformation Format 8-bit – a variable-length character encoding capable of representing the complete Unicode character set while remaining compatible with ASCII for its first 128 characters.
UTP	Unshielded Twisted Pair – network cabling consisting of pairs of insulated copper wires twisted together without an overall conductive shield.
UTS namespace	A Linux namespace isolating system identifiers such as the hostname and NIS domain name.
UUCP	Unix-to-Unix Copy – a family of protocols and programs originally developed to transfer files, email and other information between Unix systems over telephone and other point-to-point connections.
UUCP Network	A network of Unix systems using UUCP to exchange email, files and other information over scheduled or on-demand point-to-point connections.
UUID	Universally Unique Identifier – a 128-bit identifier designed to provide a practical level of uniqueness without requiring a central allocation authority.
UUID filesystem	A filesystem identifier represented by a Universally Unique Identifier and commonly used in Linux configuration so that filesystems can be identified independently of changing device names.
Variable	A named storage location or programming construct whose value can be changed during program execution.
VCS	Version Control System – software used to record and manage changes to files and projects over time.
VDSL	Very-high-bit-rate Digital Subscriber Line – a DSL technology providing higher data rates over shorter copper telephone-line distances than traditional ADSL.
VDSO	Virtual Dynamic Shared Object – a Linux mechanism allowing selected kernel-provided operations to be accessed by user-space programs without the overhead of a traditional system call where appropriate.
vector image	An image represented using geometric shapes, paths and mathematical descriptions rather than a fixed grid of pixels.
Verification	The process by which an online service confirms or marks an account as authentic or associated with a particular person, organisation, or entity.
Verified Account	An online account that has been formally confirmed by the service as belonging to the person, organisation, or entity it claims to represent.
Veronica	Very Easy Rodent-Oriented Net-wide Index to Computer Archives – an indexing and search system for Gopher menus, developed when Gopher was widely used on the Internet.
Version	A particular release or state of a piece of software, hardware, data or other technology, normally identified by a version number or name.
Version Control	A system for recording changes to files over time so that previous versions can be reviewed, compared or restored.
version control system	Software used to record and manage changes to files over time, allowing previous versions to be inspected, compared or restored.
version number	A value used to identify a particular release, revision or state of software, data or another object.
vertical privilege escalation	A privilege-escalation scenario in which a user or process obtains higher privileges than those originally granted.
VGA	Video Graphics Array – an older analogue video display standard and connector commonly associated with computer monitors.
vhost	Short for virtual host – a web-server configuration allowing multiple websites or domains to be served by the same server.
View	A recorded instance of a user accessing or displaying a piece of online content, such as a video, image, page, or post.
Views	The recorded number of times that online content has been accessed, displayed, or played, according to the measurement rules of the particular service.
Viral	Describing online content that spreads rapidly and extensively among users, often through repeated sharing, reposting, recommendation, or discussion.
Virality	The tendency or extent of online content to spread rapidly and widely between users or communities.