a.md

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A : An IPv4 address resource record in the Domain Name System (DNS). †

A List Apart : A popular online magazine that “explores the design, development, and meaning of web content, with a special focus on web standards and best practices.” A List Apart was founded in 1998. ℹ︎ alistapart.com

A/B testing : A user experience research methodology. A/B tests consist of a randomized experiment with two variants, A and B. A/B testing includes the application of statistical hypothesis testing or “two-sample hypothesis testing” as used in the field of statistics. It is a way to compare two versions of a single variable, typically by testing a subject’s response to variant A against variant B, and determining which of the two variants is more effective. †

A11Y : → Accessibility

AAA : → Arrange, Act, Assert

AAAA : An IPv6 address resource record in the Domain Name System (DNS). †

Above the fold : The part of a web page that is visible without scrolling.

Absolute domain name : → Fully qualified domain name

Abstract Data Type : A mathematical model for data types, where a data type is defined by its behavior (semantics) from the point of view of a user of the data, specifically in terms of possible values, possible operations on data of this type, and the behavior of these operations. †

Abstraction : A way to reduce complexity and allow efficient design and implementation in complex software systems. Abstractions hide the technical complexity of systems behind simpler APIs. ‡

Accelerated Mobile Pages : A web component framework and a website publishing technology developed by Google which has the mission to “provide a user-first format for web content.” The AMP framework consists of three components: AMP HTML, which is standard HTML markup with web components, AMP JavaScript, which manages resource loading, and AMP caches, which serve and validate AMP pages. Most AMP pages are delivered by Google’s AMP cache. AMP was released in 2015. † ℹ︎ amp.dev

Accept-CH : An HTTP header that is used to specify which Client Hints headers a client should include in subsequent requests. ‡

Acceptance Test-Driven Development : A development methodology based on communication between the business customers, the developers, and the testers. ATDD aids developers and testers in understanding the customer’s needs prior to implementation, and allow customers to be able to converse in their own domain language. †

Acceptance testing : A test conducted to determine if the requirements of a specification or contract are met. In systems engineering it may involve black-box testing performed on a system prior to its delivery. In software testing the ISTQB (International Software Testing Qualifications Board) defines acceptance testing as formal testing with respect to user needs, requirements, and business processes conducted to determine whether a system satisfies the acceptance criteria and to enable users, customers, or other authorized entities to determine whether to accept the system. Acceptance testing is also known as user acceptance testing (UAT), end user testing, operational acceptance testing (OAT), acceptance test-driven development (ATDD), or field (acceptance) testing. Acceptance criteria are the criteria that a system or component must satisfy in order to be accepted by a user, customer, or other authorized entity. †

Access control : The selective restriction of access to a place or other resource, while access management describes the process. The act of accessing may mean consuming, entering, or using. †

Access Control List : A list of permissions associated with an object. An ACL specifies which users or system processes are granted access to objects, as well as what operations are allowed on given objects. Each entry in a typical ACL specifies a subject and an operation. †

Access key : In accessibility, a shortcut to jump to a specific web page via the keyboard. Access keys were introduced in 1999 and quickly achieved near-universal browser support. † : In computer security, security credentials that consist of an access key ID and a secret access key.

Access logs : → Server logs

Access token : A token that contains the security credentials for a login session and that identifies a user, a user’s groups, a user’s privileges, and, in some cases, a particular application. Typically, one may be asked to enter an access token (e.g., 40 random characters) rather than the usual password (an access token should therefore be kept secret just like a password). †

Accessibility : The design and development of products, devices, services, and environments so that they are usable by people with disabilities. In the context of the Web it means to make information and services usable by as many people as possible. †

Accessibility Conformance Testing : A rule format for the testing of conformance with accessibility standards. ℹ︎ w3.org/WAI/standards-guidelines/act

Accessibility Object Model : A representation of the DOM that is being used by assistive technology. ℹ︎ wicg.github.io/aom/spec

Accessibility tree : → Accessibility Object Model

Accessible Rich Internet Applications : A collection of roles, states, and properties that define accessible user interface elements and can be used to improve the accessibility and interoperability of web content and applications. ℹ︎ w3.org/TR/wai-aria

ACID : → Atomicity, Consistency, Isolation, Durability

Acid tests : A range of web standards compliance tests that were set up in 1999 (Acid1), 2005 (Acid2), and 2008 (Acid3). ℹ︎ acidtests.org

ACK : A signal that is passed between communicating processes, computers, or devices to signify acknowledgement, or receipt of message, as part of a communications protocol like the Transmission Control Protocol (TCP). †

ACL : → Access Control List

ACM : → Association for Computing Machinery

Acq-hiring : → Acqui-hiring

Acqui-hiring : The process of acquiring a company primarily to recruit its employees, rather than its products or services. “Acqui-hiring” is a portmanteau of “acquisition” and “hiring.” The term was first used in 2005. †

ACSS : → Atomic CSS

ACT : → Accessibility Conformance Testing

Action item : → Todo

ActionScript : An object-oriented programming language originally developed by Macromedia (later acquired by Adobe). ActionScript is influenced by HyperTalk, the scripting language for HyperCard. It is now an implementation of ECMAScript, though it originally arose as a sibling, both being influenced by HyperTalk. ActionScript is used primarily for the development of websites and software targeting the Adobe Flash Player platform, used on web pages in the form of embedded SWF files. †

Active redundancy : A design concept that increases operational availability and that reduces operating cost by automating critical maintenance actions. †

Active Server Pages : A server-side script engine for dynamically generated web pages. ASP can be written in a scripting language such as VBScript, JScript, or PerlScript. ASP were introduced in 1996 by Microsoft. †

Active Users : A performance metric for the success of an Internet product such as a social networking service, online game, or mobile app. It measures how many users visit or interact with the product or service over a given interval. This metric is commonly assessed per month as monthly active users (MAU), per week as weekly active users (WAU), or per day as daily active users (DAU). †

ActiveX : A software framework that allows applications to share information and functionality, based on the Component Object Model (COM) and Object Linking and Embedding (OLE). ActiveX was introduced in 1996 by Microsoft.

Adaptive : An aspect of or synonym for agile development.

Adaptive loading : The loading of web resources depending on the connection type and speed.

Adaptive technology : Technology specifically designed for and used by people with disabilities. Adaptive technology often refers to electronic and information technology access. It is a subset of assistive technology. †

Addon : → Plugin

Address Resolution Protocol : A communication protocol used for discovering the link layer address, such as a MAC address, associated with a given internet layer address, typically an IPv4 address. This mapping is a critical function in the Internet protocol suite. ARP was defined in 1982 by RFC 826, which is Internet Standard STD 37. †

Adobe ColdFusion : → ColdFusion

Adobe Dreamweaver : → Dreamweaver

Adobe Flash : → Flash

Adobe Photoshop : → Photoshop

ads.txt : An initiative from the IAB Technology Laboratory that specifies an “ads.txt” text file that companies can host on their web servers, listing the other companies authorized to sell their products or services. This is designed to allow online buyers to check the validity of the sellers from whom they buy, for the purposes of Internet fraud prevention. ads.txt was introduced in 2017. †

ADT : → Abstract Data Type

Advanced Encryption Standard : A specification for the encryption of electronic data established in 2001 by the U.S. National Institute of Standards and Technology (NIST). AES is a subset of the Rijndael block cipher developed by Vincent Rijmen and Joan Daemen. For AES, NIST selected three members of the Rijndael family, each with a block size of 128 bits, but three different key lengths: 128, 192, and 256 bits. †

Advanced Package Tool : A software user interface that works with core libraries to handle the installation and removal of software on Debian, Ubuntu, and related Linux distributions. APT simplifies the process of managing software on Unix-like computer systems by automating the retrieval, configuration, and installation of software packages. †

Advanced Persistent Threat : A stealthy threat actor, typically a nation state or state-sponsored group, which gains unauthorized access to a computer network and remains undetected for an extended period. In recent times, the term may also refer to non-state-sponsored groups conducting large-scale targeted intrusions for specific goals. The median time an APT attack goes undetected differs widely between regions. †

AES : → Advanced Encryption Standard

Affordance : Those action possibilities that are readily perceivable by an actor, that is, an affordance suggests how an object may be interacted with. For example, an underlined word on a web page has the affordance of being clickable. †

Agile : An umbrella term for approaches to project management and software development under which self-organizing, cross-functional teams cooperate with customers and users to produce requirements and solutions. Agile advocates adaptive planning, evolutionary development, early delivery, continuous improvement, and encourages rapid and flexible response to change. †

Agile Manifesto : → Manifesto for Agile Software Development

AirMosaic : An early commercial web browser based on the NCSA Mosaic browser. AirMosaic was released in 1994. †

AJAX/Ajax : → Asynchronous JavaScript and XML

ALA : → A List Apart

ALGOL : → Algorithmic Language

Algorithm : A finite sequence of well-defined, computer-implementable instructions, typically to solve a class of problems or to perform a computation. Algorithms are unambiguous specifications for performing calculation, data processing, automated reasoning, and other tasks. †

Algorithmic Language : A family of imperative computer programming languages, originally developed in the mid-1950s, which greatly influenced many other languages and was the standard method for algorithm description used by the Association for Computing Machinery (ACM) in textbooks and academic sources for more than 30 years. †

Aliasing : An effect that causes different signals to become indistinguishable (or aliases of one another) when sampled. Aliasing also often refers to the distortion or artifact that results when a signal reconstructed from samples is different from the original continuous signal. Aliasing can occur in signals sampled in time, for instance digital audio, and is referred to as temporal aliasing. It can also occur in spatially sampled signals (e.g., moiré patterns in digital images); this type of aliasing is called spatial aliasing. Aliasing is generally avoided by applying low pass filters or anti-aliasing filters (AAF) to the input signal. †

Almost standards mode : → Almost strict mode

Almost strict mode : A third web browser compatibility mode (beside strict and quirks mode) which maintains the “traditional” vertical sizing of table cells according to the CSS 2 specification, and which treats images like block elements. †

ALPN : → Application-Layer Protocol Negotiation

Alternate style sheet : A style sheet mutually exclusive to other style sheets, which can be selected for alternative styling. An alternate style sheet is indicated through the alternate keyword, as in <link rel="alternate stylesheet" href=example.css title=Example>.

Amaya : A web editor with browsing capabilities. Amaya was developed by the World Wide Web Consortium (W3C) and INRIA from 1996 to 2012.

Amazon Resource Name : A unique identifier for an Amazon Web Services (AWS) resource. An ARN follows the format arn:partition:service:region:account-id:resource-id, arn:partition:service:region:account-id:resource-type/resource-id, or arn:partition:service:region:account-id:resource-type:resource-id.

Amazon Route 53 : → Route 53

Amazon S3 : → S3

Amazon Silk : → Silk

Amazon Simple Queue Service : → SQS

Amazon Simple Storage Service : → Amazon S3

Amazon SQS : → SQS

Amazon Virtual Private Cloud : → Amazon VPC

Amazon VPC : A commercial cloud computing service that provides users a virtual private cloud, by provisioning a logically isolated section of the Amazon Web Services (AWS) cloud. † ℹ︎ aws.amazon.com/vpc

Amazon Web Services : A subsidiary of Amazon that provides on-demand cloud computing platforms and APIs on a metered pay-as-you-go basis. In aggregate, these cloud computing web services provide a set of primitive abstract technical infrastructure and distributed computing building blocks and tools. AWS technology is implemented at server farms throughout the world. † ℹ︎ aws.amazon.com

AMD : → Asynchronous Module Definition

American National Standards Institute : A private non-profit organization that, per its mission, “enhances both the global competitiveness of U.S. business and the U.S. quality of life by promoting and facilitating voluntary consensus standards and conformity assessment systems, and safeguarding their integrity.” The ANSI was founded in 1918. ℹ︎ ansi.org

American Standard Code for Information Interchange : A character encoding standard for electronic communication. ASCII was conceived in 1960 and published in 1963 by the ASA (American Standards Association), now ANSI.

AMP : → Accelerated Mobile Pages

Analytics : → Web analytics

Anchor : Technical name for a link, usually referring to the a element.

Angular : A TypeScript-based web application framework developed by Google and a community of individuals and corporations. Angular is a complete rewrite from the same team that built AngularJS. Angular was released in 2016. † ℹ︎ angular.io

AngularJS : A JavaScript-based frontend web framework mainly maintained by Google and a community of individuals and corporations to address challenges encountered in developing single-page applications (SPAs). AngularJS aims to simplify both the development and the testing of such applications by providing a framework for client-side model-view-controller (MVC) and model-view-viewmodel (MVVM) architectures, along with components commonly used in rich Internet applications. AngularJS was first released in 2010 and makes for the frontend part of the MEAN stack. Google no longer updates AngularJS, and the Angular team recommends upgrading to Angular as the best path forward. † ℹ︎ angularjs.org

Animation : A method in which images and graphics are manipulated to appear as moving. In web development, animations are often created using CSS (CSS Animations, CSS Transitions) or JavaScript. †

Anonymous block box : Within a block container box, a block-level box forced by the presence of other block-level boxes. In <div>Some text<p>More text</div>, “Some text” resides in an anonymous block-level box because <p> spawns a block-level box.

Anonymous block element : → Anonymous block box

Anonymous function : A function definition that is not bound to an identifier. Anonymous functions are often arguments being passed to higher-order functions, or used for constructing the result of a higher-order function that needs to return a function. If the function is only used once, or a limited number of times, an anonymous function may be syntactically lighter than using a named function. Anonymous functions are ubiquitous in functional programming languages and other languages with first-class functions. †

Anonymous inline box : An inline box that does not have an associated inline-level element.

Anonymous inline element : Any text that is directly contained inside a block container element that is not inside an inline element.

Anonymous text : Any string of characters that is not contained within an inline element.

ANSI : → American National Standards Institute

Anti-pattern : A common response to a recurring problem that is usually ineffective and risks being highly counterproductive, and that has more negative than positive consequences. †

AOM : → Accessibility Object Model

AOMedia Video 1 : A video coding format initially designed for video transmissions over the Internet. AV1 was developed as a successor to VP9 by the Alliance for Open Media (AOMedia), a consortium founded in 2015. † ℹ︎ aomedia.org/av1-features

Apache : → Apache HTTP Server

Apache HTTP Server : A cross-platform web server. The Apache server was first released in 1995. ℹ︎ httpd.apache.org

Apache Maven : → Maven

Apache Subversion : → Subversion

Apache Tomcat : → Tomcat

Apache Weex : → Weex

API : → Application Programming Interface

API gateway : An entry point for a system of application programming interfaces (APIs) that takes care of request routing as well as protocol translation. An API gateway also helps mitigate backend issues, for example by offering fallback or cached data.

App : → Application

App shell : The minimal HTML, CSS, and JavaScript necessary to provide a site or app user interface.

Apple Safari : → Safari

Apple Universal Access : → Universal Access

Applet : Any small application that performs a specific task that runs within the scope of a dedicated widget engine or a larger program, often as a plugin. Usually referring to a Java applet, a program written in the Java programming language that is designed to be placed on a web page. An applet is not a full-featured application program but intended to be easily accessible. †

Application : A computer program designed to help people perform an activity. An application differs from an operating system (which runs a computer), a utility (which performs maintenance or general-purpose chores), and a programming tool (with which computer programs are created). Depending on the activity for which it was designed, an application can manipulate text, numbers, audio, graphics, and a combination of these elements. Some application packages focus on a single task, such as word processing; others, called integrated software, include several applications. †

Application context : A top-level browsing context that has a manifest applied to it. ‡

Application Programming Interface : An interface or communication protocol between different parts of a computer program intended to simplify the implementation and maintenance of software. An API may be for a web-based system, operating system, database system, computer hardware, or software library. †

Application-Layer Protocol Negotiation : A TLS extension which indicates what application layer protocol is negotiating the encrypted connection without requiring additional round trips. ALPN was specified in 2014 as RFC 7301. ‡

APT : → Advanced Package Tool : → Advanced Persistent Threat

AR : → Augmented Reality

Arena : One of the first web browsers for Unix. Originally developed in 1993 by Dave Raggett, development continued at CERN and the World Wide Web Consortium (W3C) and subsequently by Yggdrasil Computing. Arena was used in testing the implementations for HTML 3.0, Cascading Style Sheets (CSS), Portable Network Graphics (PNG), and libwww. Arena was widely used and popular at the beginning of the World Wide Web. †

Argument : The actual input expression passed or supplied to a function, procedure, or routine in a call or invocation statement. †

ARIA : → Accessible Rich Internet Applications

ARIA roles : A set of predefined names that can be used to specify the meaning and purpose of markup elements. Roles can cover abstract use cases, widgets, document structure, landmarks, live regions, and windows, and are set using the role attribute.

ARN : → Amazon Resource Name

ARP : → Address Resolution Protocol

Arrange, Act, Assert : A pattern to organize test methods by.

Array : A data structure consisting of a collection of elements (values or variables), each identified by at least one array index or key. An array is stored such that the position of each element can be computed from its index tuple. The simplest type of data structure is a linear array, also called one-dimensional array. †

Arrow function : An anonymous function and syntactically compact alternative to a regular function expression, although without its own bindings to the this, arguments, super, or new.target keywords. ‡

ASCII : → American Standard Code for Information Interchange

ASI : → Automatic Semicolon Insertion

ASP : → Active Server Pages

ASP.NET : A server-side web application framework designed to build dynamic websites, applications, and services. ASP.NET was first released in 2002 with version 1.0 of the .NET Framework, and is the successor to Microsoft’s Active Server Pages (ASP) technology. † ℹ︎ dotnet.microsoft.com/apps/aspnet

Aspect ratio : A proportional relationship between an image’s width and height. The aspect ratio is commonly expressed as two numbers separated by a colon, as in 16:9. †

AssemblyScript : A TypeScript-based programming language (essentially JavaScript with static types) that is optimized for WebAssembly and compiled to WebAssembly using asc, the reference AssemblyScript compiler. AssemblyScript is developed by the AssemblyScript Project and the AssemblyScript community. It was first released in 2017. † ℹ︎ assemblyscript.org

Assignment : The setting or resetting of the value stored in the storage location(s) denoted by a variable name; in other words, an assignment statement copies a value into the variable. In most imperative programming languages, the assignment statement (or expression) is a fundamental construct. Today, the most commonly used notation for this basic operation has come to be x = expr (originally Superplan 1949–51, popularized by Fortran 1957 and C) followed by x := expr (originally ALGOL 1958, popularized by Pascal), although there are many other notations in use. †

Assistive technology : Assistive, adaptive, and rehabilitative devices and software for people with disabilities or the elderly population. Assistive technology can ameliorate the effects of disabilities that limit the ability to perform activities of daily living. †

Assistive Technology Service Provider Interface : A platform-neutral framework for providing bidirectional communication between assistive technologies (AT) and applications. AT-SPI is the de facto standard for providing accessibility to free and open desktops, like GNU/Linux or OpenBSD. It is led by the GNOME Project. †

Association for Computing Machinery : An international learned society for computing. The ACM was founded in 1947, and is the world’s largest scientific and educational computing community. Its motto is “Advancing Computing as a Science and Profession.” † ℹ︎ acm.org

Asynchronous : The occurrence of events independent of the main program flow. A common way for dealing with asynchrony in is to provide subroutines that return to their caller an object, sometimes called a future or promise, that represents the ongoing events. †

Asynchronous Module Definition : A specification for the JavaScript programming language. AMD defines an API that defines code modules and their dependencies, and loads them asynchronously if desired. Implementations of AMD promise website performance improvements, because AMD implementations load smaller JavaScript files, and then only when they are needed. AMD implementations also suggest fewer page errors, because developers can define dependencies that must load before a module is executed, so the module does not try to use outside code that is not available yet. † ℹ︎ github.com/amdjs/amdjs-api

Asynchronous JavaScript and XML : A set of web development techniques using web technologies on the client side to create asynchronous web applications. With AJAX, web applications can send and retrieve data from a server asynchronously (in the background) without interfering with the display and behavior of the existing page. By decoupling the data interchange layer from the presentation layer, AJAX allows web pages and applications to change content dynamically without the need to reload the entire page. In practice, modern implementations commonly utilize JSON instead of XML. †

at : A command on Unix-like operating systems, Microsoft Windows, and ReactOS used to schedule commands to be executed once, at a particular time in the future. †

AT : → Assistive technology

at-rule : A CSS statement starting with an at-keyword (@ and an identifier, as with @import). The at-rule holds until either the next semicolon or the next block.

AT-SPI : → Assistive Technology Service Provider Interface

ATAG : → Authoring Tool Accessibility Guidelines

ATDD : → Acceptance Test-Driven Development

Atlassian Bitbucket : → Bitbucket

Atlassian Jira : → Jira

Atom : An XML-based feed format consisting of two web standards, the Atom Syndication Format and the Atom Publishing Protocol (AtomPub or APP).

Atomic CSS : A CSS architecture that is based on “single-purpose units of style” applied via “short, predictable class names.” ℹ︎ acss.io

Atomicity, Consistency, Isolation, Durability : A set of properties of database transactions intended to guarantee validity even in the event of errors, power failures, etc. In the context of databases, a sequence of database operations that satisfies the ACID properties (which can be perceived as a single logical operation on the data) is called a transaction. The acronym was coined in 1983 by Andreas Reuter and Theo Härder. †

Attribute : A property of an object, element, or file. An attribute may also refer to or set the specific value for a given instance. An attribute of an object usually consists of a name and a value; of an element, a type or class name; of a file, a name and extension. Attributes should be considered metadata. †

Attribute minimization : The valid option for a Boolean attribute not to have a value if it is set (and therefore true). In XML-based languages, attribute minimization is disallowed and attributes must have a value; for example, checked is suggested to be written checked="checked".

Augmented Reality : An interactive experience of a real-world environment where the objects that reside in the real world are enhanced by computer-generated perceptual information, sometimes across multiple sensory modalities, including visual, auditory, haptic, somatosensory, and olfactory. AR can be defined as a system that fulfills three basic features: a combination of real and virtual worlds, real-time interaction, and accurate 3D registration of virtual and real objects. †

Authentication : The act of proving an assertion, such as the identity of a computer system user. In contrast with identification, the act of indicating a person or thing’s identity, authentication is the process of verifying that identity. †

Authoring tool : Software that enables the creation of digital content.

Authoring Tool Accessibility Guidelines : Guidelines for designing web content authoring tools that are accessible to authors with disabilities and designed to enable, support, and promote the production of more accessible web content by all authors. ATAG 1.0 became a W3C Recommendation in 2000, and ATAG 2.0 in 2015. ℹ︎ w3.org/TR/ATAG20

Authorization : The specifying of access rights and privileges to resources, which is related to information security and computer security in general, and to access control in particular. More formally, “to authorize” is to define an access policy. †

Automagic : A blend of “automatic” and “magic,” referring to an action that is performed automatically but also in a way as to seem magical.

Automatic Semicolon Insertion : An ECMAScript feature in which a semicolon is automatically inserted when two statements are separated by a line ending or a closing brace (}), or if a line ending follows either of break, continue, return, or throw (restricted production).

Automation : A technology by which a process or procedure is performed with minimal human assistance. Automation or automatic control is the use of various control systems for operating equipment. †

Autonomous custom element : One type of custom element for a web component. An autonomous custom element is standalone, that is, it does not inherit from standard HTML elements. Autonomous custom elements are used by literally writing them out as HTML elements. ‡

AV1 : → AOMedia Video 1

AV1 Image File Format : An image file format that uses AV1 compression algorithms. AVIF competes with HEIC which uses the same container format, built upon ISOBMFF, but HEVC for compression. Version 1.0.0 of the AVIF specification was finalized in 2019. †

Availability Zone : With Amazon Web Services (AWS), a term for one or more data centers with redundant power, networking, and connectivity. An AWS Region consists of several Availability Zones.

AVIF : → AV1 Image File Format

AWS : → Amazon Web Services

AZ : → Availability Zone

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