Web Accessibility Glossary
Plain-language definitions of 100+ terms you will meet in accessibility work — standards like WCAG and EN 301 549, technologies like ARIA and screen readers, and legal concepts like the ADA, Section 508, and the European Accessibility Act. Jump to a letter below or scroll through the full list.
A
Accessibility Overlay
A third-party widget or script that claims to make a website accessible automatically by injecting JavaScript fixes at page load. Overlays cannot repair the underlying code, frequently interfere with screen readers and keyboard navigation, and sites using them are still regularly named in accessibility lawsuits. Read our guide to accessibility overlays before considering one.
Accessibility Statement
A public page that describes an organization's commitment to accessibility, the standard it targets (usually WCAG 2.1 or 2.2 AA), any known limitations, and how users can report barriers. Many laws, including the European Accessibility Act and the EU Web Accessibility Directive, require one. You can create one in minutes with our accessibility statement generator.
Accessibility Tree
A simplified, parallel version of the DOM that the browser builds and exposes to assistive technology. Each node carries an element's name, role, state, and properties — a screen reader reads this tree, not your raw HTML. Semantic markup and correct ARIA usage are what keep the accessibility tree accurate.
Accessible Name
The text label that assistive technology announces for an element, such as "Search" for a magnifying-glass button. It is computed from sources like element content, the alt attribute, an associated <label>, aria-labelledby, or aria-label, following the accessible name computation algorithm. Every interactive element needs one; see our ARIA reference for how the naming attributes work.
ADA (Americans with Disabilities Act)
The landmark 1990 US civil rights law prohibiting discrimination against people with disabilities. Courts have widely applied Title III (public accommodations) to websites and apps, making the ADA the legal basis for most US digital accessibility lawsuits. A 2024 Department of Justice rule also requires state and local governments to meet WCAG 2.1 AA under Title II.
Alt Text (Alternative Text)
A short text description of an image, supplied through the alt attribute, that screen readers announce in place of the image and that displays if the image fails to load. Good alt text conveys the image's purpose in context; purely decorative images should get an empty alt="" so they are skipped. Try our alt text generator to write better descriptions faster.
APCA (Accessible Perceptual Contrast Algorithm)
A modern contrast model, developed as a candidate method for WCAG 3, that scores text contrast on a perceptual lightness scale (Lc) instead of WCAG 2's simple luminance ratio. APCA accounts for font size, weight, and polarity (light-on-dark vs dark-on-light), so it better matches how people actually perceive readability. It is not yet a normative requirement — WCAG 2 ratios still govern conformance, which you can test with our contrast checker.
ARIA (Accessible Rich Internet Applications)
A W3C specification (formally WAI-ARIA) of roles, states, and properties that supplement HTML so custom widgets and dynamic content make sense to assistive technology. ARIA only changes what screen readers perceive — it adds no keyboard behavior — so the first rule of ARIA is to prefer native HTML elements when they exist. Explore every role and attribute in our interactive ARIA reference.
Assistive Technology (AT)
Any hardware or software that people with disabilities use to operate computers and browse the web. Examples include screen readers, screen magnifiers, refreshable braille displays, switch devices, eye trackers, and voice control software. Accessible websites work because they expose structure and semantics that assistive technology can interpret.
ATAG (Authoring Tool Accessibility Guidelines)
W3C guidelines for the tools people use to create web content — CMSs, page builders, WYSIWYG editors, and code editors. ATAG 2.0 has two parts: the authoring tool's own interface must be accessible, and the tool should help authors produce accessible content, for example by prompting for alt text.
Audio Description
Additional narration added to video that describes important visual information — actions, on-screen text, scene changes — for people who are blind or have low vision. WCAG Success Criterion 1.2.5 (Level AA) requires audio description for prerecorded video content. Descriptions are usually timed to fit natural pauses in dialogue.
Accessible Description
The supplementary text assistive technology can read after an element's name, computed from aria-describedby, aria-description or the title attribute. A password field named "Password" with a description of "At least twelve characters" announces both. It is optional where the accessible name is not.
Accessible Name Computation (accname)
The W3C algorithm that decides what text names an element, in a fixed order: aria-labelledby, then aria-label, then native sources such as a label element, alt text or the control's own text, then title. Browsers, screen readers, testing libraries and AI agents all rely on it. Try it with the accessible name previewer.
Agentic Browser (Browser-Use Agent)
An AI system that operates a website on a person's behalf by reading the page's accessibility tree and issuing clicks and keystrokes. Anthropic's browser-use tool, OpenAI's computer-using agent and Google's Mariner all work this way, so a control without an accessible name is as invisible to them as it is to a screen reader.
Accessibility Conformance Report (ACR)
The completed document produced from a VPAT template, stating criterion by criterion whether a product supports, partially supports or does not support each requirement of WCAG, Section 508 or EN 301 549. Buyers ask for it in procurement; it is a claim, not a certification. See the VPAT guide.
Automated Accessibility Testing
Software that inspects markup or a rendered page for machine-detectable failures such as missing alt text, empty links, unlabelled fields and low contrast. Tools such as axe, WAVE, Lighthouse and IBM Equal Access find a minority of WCAG issues and cannot judge whether a name is meaningful or a task is completable. See automated vs manual testing.
Auxiliary Aids and Services
The ADA's term for the means of making communication accessible: interpreters, captioning, braille, and, in the Justice Department's view, accessible electronic technology. A public accommodation must provide them unless doing so would be an undue burden or fundamentally alter the service.
B
Braille Display
A hardware device with a row of refreshable cells that raise and lower pins to show, in braille, the text a screen reader is reading. Used by deafblind people and by many blind professionals for reading precision. It can only render what the page exposes as text.
C
Captions (Open vs Closed)
Text versions of the spoken audio and important sounds in video, displayed in sync with playback, primarily for people who are deaf or hard of hearing. Closed captions can be turned on and off by the viewer, while open captions are permanently burned into the video image. WCAG Success Criterion 1.2.2 (Level A) requires captions for prerecorded video with audio.
Cognitive Accessibility
Designing content so it works for people with cognitive and learning disabilities, including memory, attention, reading, and executive-function differences. Practical techniques include plain language, consistent navigation, generous time limits, clear error messages, and avoiding unnecessary complexity. The W3C's COGA task force publishes detailed guidance in "Making Content Usable for People with Cognitive and Learning Disabilities."
Color Contrast Ratio
A measure of the luminance difference between foreground text and its background, expressed on a scale from 1:1 (identical) to 21:1 (black on white). WCAG 2 Level AA requires at least 4.5:1 for normal text and 3:1 for large text; user interface components and graphics need 3:1. Measure any color pair instantly with our color contrast checker.
Conformance Level (A / AA / AAA)
WCAG's three tiers of conformance. Level A covers the most basic barriers, Level AA is the standard referenced by virtually every law and contract worldwide, and Level AAA is the strictest tier, which even the W3C says may not be achievable for all content. Conformance is cumulative — meeting AA means meeting every A and AA success criterion. See how the levels fit together in our WCAG hub.
CAPTCHA
A challenge intended to tell people from bots. Visual CAPTCHAs are unsolvable for blind users, and audio alternatives are often unusable; screen reader users rank CAPTCHA as the single most problematic item on the web in WebAIM's surveys. WCAG 1.1.1 requires alternatives in more than one modality.
Colour Vision Deficiency
Reduced ability to distinguish certain colours, affecting about 8% of men and 0.5% of women, most commonly red and green. WCAG 1.4.1 Use of Color requires that colour is never the only means of conveying information, which is why error states need an icon or text as well as a red outline.
Certiorari
The Supreme Court's discretionary decision to review a lower court's ruling. A denial of certiorari, as in Domino's Pizza v. Robles in October 2019, means the Court declined to hear the case; it decides nothing and creates no precedent, despite being widely reported as a ruling.
D
Decorative Image
An image that adds nothing a user needs, such as a divider or a stock photo beside text that already says everything. It should carry an empty alt attribute (alt="") so screen readers skip it. An image that carries information is an informative image and needs real alt text under WCAG 1.1.1.
Disclosure Widget
A button that shows or hides a section of content, such as an FAQ answer or an accordion panel. The button must expose aria-expanded so the state is announced, and must control the content programmatically via aria-controls. See the accordion guide.
Dynamic Content
Page content that changes after load without a full page refresh, such as search results, notifications or a loading spinner. Screen readers only learn of changes that are exposed through focus management or live regions; otherwise the change is silent. See notifications and focus management.
E
EAA (European Accessibility Act)
An EU directive (2019/882) that requires a wide range of private-sector products and services — e-commerce, banking, e-books, transport, telecoms, and more — to be accessible. Its obligations have applied to new products and services since June 28, 2025. For websites and apps, conformance is demonstrated against EN 301 549, which incorporates WCAG 2.1 Level AA.
EN 301 549
The European standard for accessibility of information and communication technology, covering websites, apps, documents, hardware, and support services. Its web requirements incorporate WCAG 2.1 Level AA. It is the harmonized standard used to show compliance with both the EU Web Accessibility Directive and the European Accessibility Act.
Effective Communication
The ADA regulation (28 CFR 36.303) requiring public accommodations to provide auxiliary aids and services so that communication with disabled people is as effective as with others. It was central to the dissent in Gil v. Winn-Dixie, which argued a website is a means of communication and so is covered.
Error Identification
WCAG 3.3.1: when an input error is detected automatically, the field in error must be identified and the error described in text. A red border alone fails; "Email address: enter an address in the form name@example.com" passes. Related to form validation.
F
Focus Indicator
The visible outline, ring, or highlight that shows which element currently has keyboard focus. WCAG Success Criterion 2.4.7 requires a visible focus indicator, and WCAG 2.2 adds minimum size and contrast expectations in 2.4.11 (Focus Not Obscured) and the AAA-level 2.4.13 (Focus Appearance). Never remove the outline without providing a clearly visible replacement — see our keyboard accessibility guide for patterns.
Focus Order
The sequence in which interactive elements receive keyboard focus as a user presses Tab. WCAG Success Criterion 2.4.3 requires that this order preserve meaning and operability — focus should move in a way that matches the logical reading order, which usually means keeping DOM order aligned with visual order.
Focus Trap (Keyboard Trap)
A situation where keyboard focus enters a component and cannot leave using the keyboard alone, which violates WCAG Success Criterion 2.1.2. The one intentional exception is a modal dialog, which deliberately contains focus while open but must always be dismissible with Escape and return focus to the triggering element on close.
Focus Visible
WCAG 2.4.7: the element that has keyboard focus must have a visible indicator. Removing the browser's outline without replacing it is one of the most common keyboard barriers, and GDS lists lack of visible focus among the top issues found in UK public sector monitoring. WCAG 2.2 adds 2.4.11 on the indicator's minimum size and contrast.
Form Label
The visible text programmatically associated with a form field, normally a label element linked by for and id. It gives the field its accessible name, gives sighted users a larger click target, and is required by WCAG 3.3.2 and 1.3.1. A placeholder is not a label: it disappears on input and is not reliably announced.
H
Heading Structure
The hierarchical outline created by h1–h6 elements. Screen reader users routinely navigate by jumping between headings, so a page should have one h1, use lower levels to nest subtopics, and avoid skipping levels (such as jumping from h2 to h4). Headings must be real heading elements, not just bold text.
High Contrast Mode (Forced Colors)
An operating-system feature — most notably Windows Contrast Themes — that replaces a site's colors with a limited, user-chosen palette to improve readability. Browsers expose it to CSS through the forced-colors media query and system color keywords. Designs should not rely on background images or subtle color differences alone, because forced-colors mode strips many of them away.
Hidden Content
Content removed from the accessibility tree with aria-hidden="true", display: none or the hidden attribute, or hidden visually only, as with a visually-hidden or sr-only class that keeps it for screen readers. Hiding a focusable element from assistive technology while leaving it in the tab order is a common failure.
I
Inclusive Design
A design methodology that considers the full range of human diversity — ability, language, culture, age, and circumstance — from the start of a project rather than retrofitting fixes later. It overlaps with accessibility but is broader: solving for permanent disabilities (one arm) also helps temporary (arm injury) and situational (holding a baby) limitations.
Image Map
An image with clickable regions defined by area elements. Each area needs its own alt text or it is an unnamed link. The 2006 Target case pleaded inaccessible image maps; the site's home page at filing had 85 areas, none with alt text.
K
Keyboard Accessibility
The principle that every piece of functionality must be operable with a keyboard alone, without requiring a mouse or specific timing (WCAG Success Criterion 2.1.1). It is foundational because screen readers, switch devices, and many other assistive technologies all drive the page through keyboard-style input. Our complete keyboard accessibility guide covers testing and common fixes.
Keyboard Trap
A state in which keyboard focus enters a component and cannot leave it with the keyboard, failing WCAG 2.1.2. Distinct from a deliberate focus trap inside an open modal, which must release focus when the modal closes.
L
Landmark Regions
Major page areas — banner, navigation, main, complementary, contentinfo, search — that assistive technology users can jump between directly. HTML5 elements like <header>, <nav>, <main>, <aside>, and <footer> create landmarks automatically. Every page should have exactly one main landmark, and repeated landmarks (like multiple navs) should be given distinguishing labels; see the landmark roles in our ARIA reference.
Live Region
A page area marked with aria-live (or a role like status or alert) whose content changes are announced automatically by screen readers, even when focus is elsewhere. Use aria-live="polite" for non-urgent updates such as search-result counts, and assertive (or role="alert") only for critical messages, because assertive announcements interrupt whatever the user is doing.
Label in Name
WCAG 2.5.3: where a control has a visible text label, its accessible name must contain that text. A button that shows "Search" but has aria-label="Submit query" fails, because a voice control user who says "click Search" gets nothing.
Language of Page
WCAG 3.1.1: the default human language of a page must be programmatically determined, normally with the lang attribute on the html element. Without it screen readers may pronounce the page with the wrong voice and rules. Pages with no lang attribute are still common, including on large retail sites.
Link Purpose
WCAG 2.4.4: the purpose of each link must be determinable from its text alone or with its surrounding context. "Read more" repeated five times is the classic failure; screen reader users often navigate by pulling up a list of links out of context.
M
Motion Actuation
WCAG 2.5.4: functions triggered by moving or tilting the device, such as shake to undo, must also be available through the interface and must be switchable off, because tremor and mounted devices trigger them accidentally.
N
Name, Role, Value
The requirement (WCAG Success Criterion 4.1.2) that every user interface component exposes its accessible name, its role (button, checkbox, tab), and its current states and values to assistive technology. Native HTML elements do this for free; custom widgets built from divs must supply all three through ARIA and keep them updated as state changes.
Nexus Test
The rule, first applied to websites in NFB v. Target in 2006, that Title III of the ADA reaches a website only where its inaccessibility impedes the goods and services of a physical place of public accommodation. Applied by the Ninth Circuit in Robles v. Domino's. See the case law reference.
Non-text Content
WCAG 1.1.1: all images, icons, charts and other non-text content must have a text alternative that serves the equivalent purpose, except decorative content, which is marked so that it is ignored. Missing alternative text was found on 53.1% of the top million home pages in 2026.
O
Orientation
WCAG 1.3.4: content must not be locked to portrait or landscape unless the orientation is essential, because people with mounted devices, such as wheelchair users, cannot rotate them.
P
PDF/UA
The ISO 14289 standard for universally accessible PDF documents. A conforming PDF is fully tagged with a logical structure tree, includes alternative text for images, marks the document language, and sets a correct reading order so screen readers can navigate it like a web page. Check your documents with our PDF accessibility checker.
POUR
The four principles that organize all of WCAG: Perceivable, Operable, Understandable, and Robust. Content must be perceivable through more than one sense, operable by keyboard and other inputs, understandable in language and behavior, and robust enough to work with current and future assistive technologies. Every WCAG success criterion lives under one of these four principles.
prefers-reduced-motion
A CSS media query that detects when a user has asked their operating system to minimize animation, often because motion triggers vestibular disorders, migraines, or nausea. Sites should use it to disable or tone down parallax effects, auto-playing animation, and large transitions. It complements WCAG 2.3.3 (Animation from Interactions).
Programmatically Determined
A phrase used throughout WCAG meaning that information can be reliably extracted by software — including assistive technology — from the markup itself, rather than existing only visually. A label is programmatically determined when it is linked with a <label> element or ARIA attribute; a heading is programmatically determined when it uses an actual heading tag rather than large bold text.
Pause, Stop, Hide
WCAG 2.2.2: any moving, blinking or auto-updating content that starts automatically and lasts more than five seconds must have a control to pause, stop or hide it. Carousels and tickers are the usual failures. See the carousel patterns.
Place of Public Accommodation
The ADA's term for private businesses open to the public, listed in twelve categories in 42 U.S.C. 12181(7), all of them physical. Whether a website is one, or is a service of one, is the question every US website case turns on. The case law reference tracks each circuit's answer.
Pointer Gestures
WCAG 2.5.1: functions that use multipoint or path-based gestures, such as pinch to zoom or swipe to delete, must also work with a single pointer without a path, because switch, head-pointer and tremor users cannot perform them.
Public Sector Bodies Accessibility Regulations (PSBAR)
The UK regulations (2018) implementing the EU Web Accessibility Directive, requiring public sector websites and apps to meet the accessibility requirement (in practice WCAG 2.2 AA) and publish a compliant accessibility statement. Monitored by GDS, which found only 39 of 593 statements fully compliant in its first round. See the statement checker.
Parsing (WCAG 4.1.1)
A WCAG 2.0 and 2.1 criterion about valid markup, removed in WCAG 2.2 because modern browsers repair broken HTML consistently. Duplicate ids and unclosed elements are still worth fixing because they break label associations and aria references.
Q
Query Fan-out
The way AI answer engines decompose a question into many sub-queries, retrieving a passage for each before synthesising an answer. It is why a page is cited for a single self-contained passage that answers a sub-question, and why every figure on the statistics page is written to stand alone.
R
Reading Level
WCAG 3.1.5 (AAA): where text requires more than lower secondary education reading ability, a simpler version or summary should be available. Plain language benefits people with cognitive disabilities, the largest disability group in US data at 13.9% of adults. See the cognitive accessibility guide.
Redundant Entry
WCAG 2.2's 3.3.7: information a user has already entered in the same process must be auto-populated or selectable, not typed again, unless re-entry is essential such as confirming a password.
Remediation
The work of fixing accessibility failures in code, content or design after they are found. Distinct from an audit, which finds them, and from an overlay, which claims to mask them. The only remediation estimate ever given in evidence at a web accessibility trial was $37,000 or less, in Gil v. Winn-Dixie.
S
Screen Magnifier
Software that enlarges a portion of the screen, used by people with low vision. Examples include ZoomText, Windows Magnifier, and macOS Zoom. Because magnifier users see only a small slice of the page at a time, placing error messages or updates far from the user's point of focus can make them easy to miss entirely.
Screen Reader
Software that converts on-screen content into synthesized speech or braille output, used primarily by people who are blind or have low vision. Major screen readers include JAWS and NVDA on Windows, VoiceOver on Apple platforms, and TalkBack on Android. They navigate via the accessibility tree, so semantics matter more than visuals — learn how to test in our screen reader testing guide.
Section 508
A US federal law (part of the Rehabilitation Act) requiring federal agencies to make their electronic and information technology accessible, which in practice extends to vendors selling to the government. The 2017 "refresh" of the Section 508 standards incorporates WCAG 2.0 Level AA as the technical benchmark for web content.
Semantic HTML
Using HTML elements for their intended meaning — <button> for buttons, <nav> for navigation, <table> for tabular data — instead of generic <div> and <span> containers styled to look the part. Semantic elements come with built-in roles, keyboard behavior, and accessibility tree entries for free. Our accessible component patterns show semantic-first implementations of common UI.
Skip Link
A link, usually the first focusable element on a page, that lets keyboard users jump straight to the main content instead of tabbing through the entire header and navigation on every page. It is typically visually hidden until it receives focus. Skip links are the classic technique for WCAG Success Criterion 2.4.1 (Bypass Blocks).
Success Criterion
A single testable requirement in WCAG, identified by number and name — for example, 1.4.3 Contrast (Minimum). Each success criterion is assigned a conformance level (A, AA, or AAA) and is written so that testers can objectively determine pass or fail. WCAG 2.2 contains 86 success criteria in total; browse them all in our WCAG reference.
Switch Access
An input method for people with significant motor disabilities that uses one or more physical switches — pressed by hand, head, foot, or breath — instead of a keyboard or mouse. Software scans through interface options and the user activates a switch to select. Switch access depends entirely on content being keyboard-operable, since switches map to keyboard-style focus and activation.
Sensory Characteristics
WCAG 1.3.3: instructions must not rely solely on shape, colour, size, position or sound. "Click the round button on the right" fails for a screen reader user; "click Submit" passes.
Serial Plaintiff
A plaintiff who files many similar accessibility lawsuits. Courts have sanctioned abusive schemes, and disability organisations including the NFB have criticised high-volume filing, while noting that the barriers pleaded are usually real. 46% of 2025 federal website cases named a defendant that had been sued before.
Statutory Damages
A fixed sum a statute awards per violation without proof of loss. Title III of the ADA has none; California's Unruh Act awards a minimum of $4,000 per violation, which is why the money in Domino's and Target came from California law.
Status Message
WCAG 4.1.3: a message that reports a result or progress without taking focus, such as "3 items in your basket" or "Search returned 12 results", must be exposed to assistive technology, normally with a live region, so screen reader users hear it without moving.
Structured Negotiation
A method of resolving accessibility claims through a collaborative process with a written agreement instead of a lawsuit, associated with the lawyer Lainey Feingold. Safeway's 2013 commitment to WCAG 2.0 AA for its grocery site came from a structured negotiation with nine blind customers.
T
Tab Order
The order in which focus moves through interactive elements when the user presses the Tab key. By default it follows DOM source order, which is why placing elements visually with CSS while leaving the DOM in a different order creates confusing navigation. Tab order should always match the expected visual and logical reading order.
tabindex
An HTML attribute that controls whether and how an element participates in keyboard focus. tabindex="0" adds an element to the natural tab order, tabindex="-1" makes it focusable only via script (useful for moving focus to headings or dialogs), and positive values like tabindex="5" override natural order and are strongly discouraged because they create unpredictable jumps.
Text Spacing
WCAG Success Criterion 1.4.12 requires that content lose nothing when users override typography to at least: line height 1.5× the font size, paragraph spacing 2×, letter spacing 0.12×, and word spacing 0.16×. People with dyslexia and low vision often apply these overrides, so layouts must not clip or overlap text when spacing grows.
Touch Target
The tappable area of an interactive control on a touch screen. WCAG 2.2 Success Criterion 2.5.8 (Level AA) requires targets to be at least 24×24 CSS pixels or have equivalent spacing, while the AAA-level 2.5.5 recommends 44×44. Small, tightly packed targets are a major barrier for people with tremors or limited dexterity — our WCAG 2.2 checklist covers the new criteria.
Transcript
A full text version of the spoken and important non-speech audio in a recording. Transcripts are the only way audio-only content (like podcasts) reaches deaf users, they help deafblind users via braille, and they make media searchable and skimmable for everyone. WCAG 1.2.1 requires a text alternative for prerecorded audio-only content.
Target Size
WCAG 2.2's 2.5.8 (AA): pointer targets must be at least 24 by 24 CSS pixels or have that much spacing, with exceptions for inline links and essential cases. The AAA criterion 2.5.5 asks for 44 by 44. Small tap targets are among the mobile issues most often found. See 2.5.8.
Timing Adjustable
WCAG 2.2.1: where content has a time limit, users must be able to turn it off, adjust it or extend it, with limited exceptions. Session timeouts on checkout and banking flows are the common case; a warning with a way to extend passes.
Title Attribute
An HTML attribute that shows a tooltip on hover. It is the last resort in the accessible name computation, is not shown to keyboard or touch users, and is unreliable in screen readers, so it should never be the only label for a control. It is required on iframes, where it names the frame.
U
Unruh Act
California's civil rights act, which prohibits discrimination by businesses and treats any ADA violation as an Unruh violation. Because it allows statutory damages of at least $4,000 per violation plus attorney's fees, it is a primary reason such a large share of US web accessibility lawsuits are filed in California courts.
User Agent
Any software that retrieves and presents web content on behalf of a user — browsers, media players, and even assistive technologies acting alongside them. The W3C's User Agent Accessibility Guidelines (UAAG) cover this layer, complementing WCAG (content) and ATAG (authoring tools).
Undue Burden
The ADA defence that providing an auxiliary aid would involve significant difficulty or expense, judged against the resources of the whole organisation. It must be pleaded and proved. Neither Domino's nor Winn-Dixie argued it in court; Winn-Dixie's own witness testified the work was feasible.
V
Voice Control
Assistive technology that lets people operate a device by speaking commands, such as Dragon NaturallySpeaking, Apple Voice Control, or Android Voice Access. Users typically say the visible label of a control ("click Submit"), which is why WCAG 2.5.3 (Label in Name) requires an element's accessible name to contain its visible text.
VPAT (Voluntary Product Accessibility Template)
A standardized template, published by the Information Technology Industry Council, that vendors fill out to report how well their product meets accessibility standards. The completed document is called an Accessibility Conformance Report (ACR). Editions exist for WCAG, US Section 508, EU EN 301 549, and a combined international version, and procurement teams routinely request one before purchase.
Vacated Opinion
A court decision that the court has withdrawn, so it has no precedential effect. The Eleventh Circuit's 2021 opinion that websites are not public accommodations was vacated as moot in December 2021 and binds nobody, though it is still widely cited as law. See Gil v. Winn-Dixie.
W
WAI (Web Accessibility Initiative)
The group within the W3C that develops web accessibility standards and resources. WAI produces WCAG for content, ATAG for authoring tools, UAAG for browsers, and the WAI-ARIA specification for rich applications, along with widely used educational material and the ARIA Authoring Practices Guide.
WCAG (Web Content Accessibility Guidelines)
The international standard for accessible web content, published by the W3C. WCAG 2.2 (2023) is the current version, organized under the four POUR principles into testable success criteria at levels A, AA, and AAA; WCAG 2.1 AA remains the benchmark cited by most laws. Browse every criterion in our WCAG reference or work through the WCAG 2.2 checklist.
Web Accessibility Audit
A systematic evaluation of a website or app against an accessibility standard, usually WCAG 2.1 or 2.2 AA. A thorough audit combines automated scanning (which finds roughly a third of issues) with manual keyboard testing and screen reader testing, and produces a prioritized report of failures with remediation guidance.
WCAG-EM
The W3C's Website Accessibility Conformance Evaluation Methodology, which sets out how to scope, sample and report an audit of a website against WCAG. Version 2.0, published in 2026, extends it beyond websites. Used to decide how many pages an audit should cover.
WAI-ARIA Authoring Practices Guide (APG)
The W3C's collection of design patterns showing how to build common widgets such as tabs, menus, comboboxes and dialogs with the correct roles, states and keyboard behaviour. The source most of this site's component guides are built from.
Web Accessibility Directive (EU)
Directive (EU) 2016/2102, requiring public sector websites and apps across the EU to meet EN 301 549 and publish accessibility statements, with national monitoring. The UK's PSBAR implemented it; the European Accessibility Act extends similar duties to private sector products and services.
Z
Zoom and Reflow
WCAG Success Criterion 1.4.10 requires that content reflow — rewrap into a single column without two-dimensional scrolling — when zoomed to 400% on a 1280px-wide screen (equivalent to a 320px viewport). Responsive design generally achieves this, but fixed-width layouts, data tables, and text in images commonly break it, forcing low-vision users to scroll horizontally for every line.
Put the vocabulary to work
Now that you know the terms, dig into the details: browse every success criterion in the WCAG reference, learn accessible component patterns in Learn, or test your site with our free accessibility tools.