Glossary
The terms an auditor expects you to know.
94 accessibility terms. Definition-first. Sourced.
standard
WCAG
WCAG (Web Content Accessibility Guidelines) is the W3C technical standard defining how to make web content perceivable, operable, understandable and robust for people with disabilities; the current version, WCAG 2.2, was published October 2023.
POUR
POUR is the mnemonic for WCAG's four guiding principles — Perceivable, Operable, Understandable, Robust — under which all WCAG success criteria are organised.
Success Criterion
A WCAG success criterion is a testable statement defining a specific accessibility requirement — for example "1.1.1 Non-text Content" requires text alternatives for all non-text content; WCAG 2.2 contains 87 success criteria across Levels A (30), AA (20 additional), and AAA (37 additional).
Level AA
Level AA is the middle of WCAG's three conformance levels — comprising all Level A and Level AA success criteria (50 total in WCAG 2.2) — and the legally required target referenced by virtually every national accessibility law, including ADA, EAA, Section 508, and AODA.
Level A
Level A is the minimum conformance level of WCAG, comprising 30 success criteria in WCAG 2.2; below Level A, content is not accessible at all to some user groups.
Level AAA
Level AAA is the enhanced WCAG conformance level, comprising all 87 criteria across A, AA, and AAA in WCAG 2.2; W3C explicitly notes that AAA cannot be achieved for all content, so AAA conformance is recommended for parts of content rather than entire sites.
WAI
WAI (Web Accessibility Initiative) is the W3C's accessibility working group, established 1997, that develops and maintains WCAG, ARIA, ATAG, UAAG, and supporting accessibility guidance documents — the central global authority on web accessibility standards.
W3C
W3C (World Wide Web Consortium) is the international standards body founded by Tim Berners-Lee in 1994 that develops web standards including HTML, CSS, and (via WAI) WCAG; W3C standards become "Recommendations" after a multi-stage open-consensus process involving Working Drafts and Candidate Recommendations.
ATAG
ATAG (Authoring Tool Accessibility Guidelines) is a W3C standard, currently at version 2.0, defining accessibility requirements for authoring tools — content management systems, page builders, IDEs, editors — both for use by authors with disabilities and for producing accessible output.
UAAG
UAAG (User Agent Accessibility Guidelines) is a W3C standard, currently at version 2.0 (Note status), defining accessibility requirements for user agents — browsers, media players, plugins — to ensure they communicate accessibly with assistive technologies and provide accessible UI to all users.
PDF/UA
PDF/UA-1 (ISO 14289-1) is the international standard for accessible PDF — specifying tagged document structure, reading order, alt text, navigation, form field accessibility, and metadata — and the technical benchmark referenced by Section 508 and most national accessibility laws for PDF compliance.
WAI-ARIA
WAI-ARIA is the formal W3C specification of ARIA — currently at version 1.2 — defining roles, states, properties, and behaviours that supplement HTML to communicate the semantics of custom interactive widgets to assistive technologies.
WCAG 3.0
WCAG 3.0 is a forthcoming W3C accessibility standard currently in Working Draft — introducing a new conformance model (Bronze, Silver, Gold scoring) intended to address more disability categories and content types than the existing pass/fail success-criterion model of WCAG 2.x; not expected to reach Recommendation status before 2027.
technology
ARIA
ARIA (Accessible Rich Internet Applications) is a W3C specification of HTML attributes — roles, states, and properties — that supplement native HTML semantics to communicate the structure and behaviour of custom interactive widgets to assistive technologies such as screen readers.
Screen Reader
A screen reader is an assistive-technology application that converts the visual content of a screen — text, images, controls — into synthesised speech or refreshable braille output for people who are blind or have low vision; the dominant screen readers are JAWS (Windows), NVDA (Windows), VoiceOver (Apple), TalkBack (Android), and ChromeVox.
NVDA
NVDA (NonVisual Desktop Access) is a free, open-source Windows screen reader developed by NV Access (Australia) since 2006; second-most-used screen reader globally per WebAIM's 2024 survey (~38% share) and the standard reference for accessibility testing because it is free and easily installed.
JAWS
JAWS (Job Access With Speech) is a commercial Windows screen reader from Freedom Scientific (a Vispero company); the most-used screen reader in enterprise and government environments per WebAIM's 2024 survey, with ~40% market share.
VoiceOver
VoiceOver is the screen reader built into Apple's macOS, iOS, iPadOS, watchOS, and tvOS operating systems; the standard screen reader on Apple devices and the third-most-used screen reader overall per WebAIM's 2024 survey (~12% share).
TalkBack
TalkBack is the Android screen reader maintained by Google; the dominant screen reader on Android devices and the primary testing target for Android app accessibility.
Assistive Technology (AT)
Assistive technology (AT) is hardware or software that enables a person with a disability to perform tasks they would otherwise find difficult or impossible — including screen readers, screen magnifiers, alternative input devices (switches, eye trackers, sip-and-puff), voice-recognition software, and braille displays.
Live Region
A live region is a DOM element marked with the aria-live attribute (or one of the implicit live-region roles: alert, status, log) so that updates to its content are announced by screen readers without moving keyboard focus — used for toast notifications, form validation, loading indicators and status messages.
Role (ARIA)
An ARIA role is an HTML attribute that tells assistive technology what kind of widget an element is — button, dialog, tablist, menuitem — when the native HTML element does not communicate that role semantically; ARIA defines over 70 roles in the WAI-ARIA 1.2 specification.
prefers-reduced-motion
prefers-reduced-motion is a CSS media query that detects whether the user has signalled, via OS settings, a preference for reduced motion — used to disable or simplify animations, parallax scrolling, and large-scale movement that can trigger vestibular disorders, motion sickness, or attention issues.
axe-core
axe-core is the open-source accessibility testing engine maintained by Deque Labs under the Mozilla Public Licence 2.0 — used by over 3 billion scans, integrated into Google Lighthouse, browser DevTools, and most third-party accessibility scanners — and the de facto standard rule engine for automated WCAG testing.
Lighthouse
Lighthouse is Google's open-source automated testing tool for web pages — auditing performance, accessibility, SEO, best practices, and PWA — with the accessibility audit powered by a subset of axe-core rules, providing a fast in-browser quick-check used by millions of developers.
Pa11y
Pa11y is an open-source accessibility testing CLI and library — running automated WCAG tests via headless Chrome — popular for batch site-wide scanning and CI integration; Pa11y supports both HTML CodeSniffer and axe-core rule engines.
WAVE
WAVE (Web Accessibility Evaluation Tool) is a free in-browser accessibility scanner from WebAIM that visualises accessibility issues directly on the page — using colour-coded icons to mark errors, alerts, structural elements and ARIA — and a long-running educational tool for accessibility learners.
Accessibility Overlay
An accessibility overlay is a third-party JavaScript widget injected into a website that claims to detect and remediate accessibility issues at run-time — by manipulating the DOM, presenting an accessibility-preferences panel, or both; the practice has been the subject of an organised opposition (the Overlay Fact Sheet, signed by 900+ accessibility professionals) and has not insulated user sites from ADA lawsuits.
Accessibility Widget
An accessibility widget is a UI panel — typically a floating button that opens a preferences sidebar — offering toggleable settings (text size, contrast modes, dyslexia-friendly fonts, motion preferences, language switching) for end users to customise their browsing experience; widgets can supplement source-level accessibility but do not replace it.
iOS Accessibility
iOS accessibility is Apple's comprehensive accessibility platform — VoiceOver, Dynamic Type, Switch Control, Voice Control, AssistiveTouch, Magnifier and others — supported via the UIAccessibility protocol that developers implement on each UI element to expose proper labels, traits, hints, and custom actions to assistive technologies.
Android Accessibility
Android accessibility is Google's mobile accessibility platform — TalkBack, Select to Speak, Switch Access, Voice Access, Magnification and others — supported through the AccessibilityNodeInfo API that developers populate via Views' contentDescription, labelFor, and AccessibilityDelegate.
Switch Device
A switch device is an adaptive-technology input device — a single or multi-button switch operated by hand, head, breath, or other body motion — used by people with severe motor impairments to operate a computer through scanning interfaces and switch control software (Apple Switch Control, Android Switch Access).
Eye Tracker
An eye tracker is an adaptive-technology device — typically a camera-based sensor — that translates eye movement and gaze into pointer control, enabling people with severe motor impairments to navigate digital products without physical input.
Braille Display
A refreshable braille display is an electromechanical hardware peripheral with rows of pins that raise to form braille characters — connected via USB or Bluetooth to a computer or mobile device running a screen reader — used by blind and deafblind individuals as a tactile alternative to (or supplement of) speech output.
wcag criterion
1.1.1 Non-text Content
WCAG 2.2 Success Criterion 1.1.1 Non-text Content (Level A) requires that all non-text content (images, charts, audio, video, controls) presented to the user has a text alternative that serves the equivalent purpose — with specific exceptions for decoration, formatting, time-based media, tests/exercises, and CAPTCHA (which themselves have additional requirements).
1.4.3 Contrast (Minimum)
WCAG 2.2 Success Criterion 1.4.3 Contrast (Minimum) at Level AA requires text and images of text to have a contrast ratio of at least 4.5:1 against their background, with large-scale text (18 point or 14 point bold) requiring 3:1; the WCAG 2.2 sister criterion 1.4.11 Non-text Contrast covers UI components and graphical objects at 3:1.
2.1.1 Keyboard
WCAG 2.2 Success Criterion 2.1.1 Keyboard (Level A) requires that all functionality of the content is operable through a keyboard interface without requiring specific timings for individual keystrokes — except where the underlying function requires input that depends on the path of the user's movement (e.g. freehand drawing).
2.4.7 Focus Visible
WCAG 2.2 Success Criterion 2.4.7 Focus Visible (Level AA) requires that any keyboard-operable user interface have a mode of operation where the keyboard focus indicator is visible — the bright outline or other indicator that shows which element will receive input.
2.5.5 Target Size
WCAG 2.2 Success Criterion 2.5.5 Target Size (Enhanced, Level AAA) requires that pointer targets (buttons, links) be at least 44 × 44 CSS pixels — with the related WCAG 2.2 criterion 2.5.8 Target Size (Minimum) at Level AA requiring at least 24 × 24 CSS pixels, accommodating users with motor impairments.
4.1.3 Status Messages
WCAG 2.2 Success Criterion 4.1.3 Status Messages (Level AA) requires that status messages — error confirmations, form-submit results, loading indicators — be programmatically determinable through role or properties such that they can be presented to the user by assistive technologies without receiving focus.
practice
A11y
A11y is a numeronym for "accessibility" — the letter "a", followed by 11 letters ("ccessibilit"), followed by "y" — commonly used in software engineering shorthand, GitHub labels, and documentation to refer to the practice of building usable products for people with disabilities.
Alt Text
Alt text is the textual alternative for an image, declared via the HTML alt attribute, that conveys the image's meaning to people who cannot see it — read aloud by screen readers, displayed when images fail to load, and used for search-engine indexing.
Semantic HTML
Semantic HTML is the practice of using HTML elements for their meaning rather than appearance — header, nav, main, footer, article, section, button, label — so that browsers, assistive technologies and search engines can understand the document structure without authors adding ARIA.
Landmark
A landmark is a region of a page identified to assistive technology by either a semantic HTML element (header, nav, main, aside, footer) or an explicit ARIA role (banner, navigation, main, complementary, contentinfo), allowing screen-reader users to skip directly to major sections of the page.
Skip Link
A skip link is a hidden hyperlink at the very start of a page, revealed when focused via keyboard, that lets a keyboard user bypass the navigation and jump directly to the main content — a WCAG 2.4.1 Bypass Blocks technique.
Focus Management
Focus management is the practice of programmatically directing keyboard focus to appropriate elements during dynamic interactions — opening a modal, navigating to a new route in an SPA, revealing newly added content — so that keyboard and screen-reader users follow the same logical sequence as visual users.
Focus Trap
A focus trap is the technique of constraining keyboard focus to a contained element — typically a modal dialog — by cycling focus from the last focusable element back to the first when Tab is pressed at the boundary, and returning focus to the triggering element when the modal is dismissed.
Tab Order
Tab order is the sequence in which interactive elements receive keyboard focus when the user presses the Tab key — derived from DOM order by default and modifiable (with caution) via the tabindex attribute; logical tab order is a WCAG 2.4.3 Focus Order requirement at Level A.
Keyboard Navigation
Keyboard navigation is the ability to operate a digital product using only a keyboard — Tab to move between interactive elements, Enter / Space to activate, arrow keys within composite widgets — without requiring a pointing device; a WCAG 2.1.1 Level A requirement.
Captions
Captions are synchronised text alternatives for the audio content of video — including dialogue and meaningful non-speech audio (laughter, music descriptions, sound effects) — required by WCAG 1.2.2 at Level A for pre-recorded video and 1.2.4 at Level AA for live video.
Transcript
A transcript is a text rendering of the audio (and ideally video description) of recorded content — required by WCAG 1.2.1 at Level A for audio-only and video-only content, and a useful supplement to captions for video that provides searchable, indexable text.
Audio Description
Audio description is a separate audio track providing narrated description of meaningful visual content in video that is not conveyed through dialogue — required by WCAG 1.2.5 at Level AA for pre-recorded video where significant visual information is presented.
Contrast Ratio
Contrast ratio is the numeric comparison of luminance between two colours — calculated via WCAG's luminance formula — used to evaluate text legibility against its background; WCAG 1.4.3 at Level AA requires 4.5:1 for normal text and 3:1 for large text (18pt or 14pt bold).
Accessibility Audit
An accessibility audit is a structured evaluation of a digital product against an accessibility standard (typically WCAG 2.1 or 2.2 at Level AA) — combining automated scanning, manual review, and assistive-technology testing — producing a documented list of issues, severity ratings, and remediation recommendations.
Remediation
Accessibility remediation is the process of fixing accessibility issues identified in an audit — at the source code, content, or design level — until a product meets its target conformance level, typically WCAG 2.1 or 2.2 Level AA.
Manual Testing
Manual accessibility testing is the human-led evaluation of a digital product against accessibility standards — using keyboard-only navigation, multiple screen readers (NVDA, JAWS, VoiceOver, TalkBack), zoom, and cognitive evaluation — necessary because approximately 70% of WCAG criteria cannot be reliably evaluated by automated tools.
Automated Testing
Automated accessibility testing uses software — primarily the open-source axe-core engine, plus tools like Lighthouse, WAVE, Pa11y, and IBM Equal Access — to scan for WCAG violations programmatically; useful as a regression layer in CI but able to detect only approximately 25–30% of WCAG criteria.
User Testing with People with Disabilities
Accessibility user testing engages people with disabilities — paid, with informed consent — to perform realistic tasks on a product and report usability barriers; complementary to manual auditing because it surfaces real-world friction that conformance testing alone cannot detect.
Disproportionate Burden
Disproportionate burden is the EAA exemption — codified in Article 14 and Annex VI — that allows a covered entity to claim partial exemption from accessibility requirements when conformance would impose costs disproportionate to the entity's size, importance to disabled users, or expected use; the exception must be documented and reviewed every five years or on significant change.
Mobile Accessibility
Mobile accessibility encompasses making mobile websites and native iOS / Android applications usable by people with disabilities — combining WCAG principles applied to mobile contexts, native platform accessibility APIs (Apple UIAccessibility, Android AccessibilityNodeInfo), and platform-specific patterns like dynamic type, switch control, and gesture alternatives.
PDF Accessibility
PDF accessibility is the practice of producing PDF documents that meet PDF/UA-1 (ISO 14289-1) — through tagged structure, proper reading order, alt text on images, accessible form fields and bookmarks — making the document usable by screen readers and other assistive technologies.
EPUB Accessibility
EPUB accessibility is the practice of producing EPUB ebook files that conform to the EPUB Accessibility 1.1 specification — including proper semantics via DPUB-ARIA, navigable structure, alt text, accessible media, and Schema.org accessibility metadata — required for in-scope ebooks under the European Accessibility Act.
Plain Language
Plain language is the practice of writing content in clear, simple, jargon-free prose that users can read, understand, and act on the first time — a core cognitive accessibility practice and a legal requirement for US federal government communications under the Plain Writing Act of 2010.
Heading Hierarchy
Heading hierarchy is the practice of structuring page headings (h1 through h6) in a logical nested sequence — single h1 per page, h2 for top-level sections, h3 nested within h2 — so that screen-reader users can navigate the page structure by heading level and infer document organisation.
APCA
APCA (Accessible Perceptual Contrast Algorithm) is a contrast-calculation method developed by Andrew Somers as a candidate replacement for WCAG's 2.0-era luminance contrast formula — designed to better reflect perceptual contrast across the visual range; currently being explored for inclusion in WCAG 3.0 but not yet adopted in normative WCAG.
Reading Order
Reading order is the sequence in which screen readers traverse content — determined by DOM order in HTML and tag-tree order in PDF — and required by WCAG 1.3.2 Meaningful Sequence (Level A) to be presentation-independent so that visual rearrangement (CSS, RTL) does not change the meaning of the content.
Modal Dialog
A modal dialog is a UI overlay that demands user attention before they can interact with the rest of the page — requiring an accessible implementation that traps focus inside the modal, restores focus on close, communicates its role via aria-role="dialog" or "alertdialog", and supports dismissal via Escape key.
Live Captions
Live captions are real-time text transcriptions of spoken audio during live events — webinars, lectures, broadcasts, telehealth calls — required by WCAG 1.2.4 Captions (Live) at Level AA for synchronised audio content, and produced by human stenocaptioners, automatic speech recognition (ASR), or a hybrid.
role
IAAP
IAAP (International Association of Accessibility Professionals) is a non-profit professional association that maintains the leading professional certifications for digital accessibility — CPACC, WAS, and CPWA — and is part of the G3ict global initiative for inclusive ICT.
CPACC
CPACC (Certified Professional in Accessibility Core Competencies) is the foundation-level IAAP certification covering disability awareness, accessibility standards (WCAG, ADA, EAA), and the practice of universal design — earned by passing a 100-question, 2-hour, multiple-choice exam.
WAS
WAS (Web Accessibility Specialist) is IAAP's technical-track certification for practitioners who design, build, audit, or remediate web accessibility — focusing on WCAG, ARIA, screen-reader compatibility, and remediation strategies.
CPWA
CPWA (Certified Professional in Web Accessibility) is the combined IAAP credential earned by holders of both CPACC and WAS, recognising mastery of both foundational accessibility principles and applied web accessibility practice.
IAAP CPACC
See CPACC — the IAAP Certified Professional in Accessibility Core Competencies certification.
IAAP WAS
See WAS — the IAAP Web Accessibility Specialist certification.
Fable
Fable is a Toronto-based accessibility user-testing platform that connects product teams with assistive-technology users for paid usability studies — providing a vetted panel of screen-reader, keyboard, voice-control, and switch-device users.
Knowbility
Knowbility is an Austin-based US non-profit, founded 1999, providing accessibility training, audits, and the long-running AccessU and AIR (Accessibility Internet Rally) programmes — a foundational organisation in the accessibility professional community.
WebAIM
WebAIM (Web Accessibility In Mind) is a non-profit organisation at Utah State University's Center for Persons with Disabilities — founded 1999 — providing accessibility evaluation tools (WAVE), training, the annual Screen Reader User Survey, and the WebAIM Million annual study of the top one million home pages.
condition
Blindness
Blindness is the absence of usable vision; people who are blind typically use screen readers, refreshable braille displays, voice input and keyboard-only navigation — depending on technology that requires semantic HTML, proper text alternatives, and logical keyboard support.
Low Vision
Low vision refers to significant visual impairment not corrected by standard glasses or contact lenses — including reduced acuity, limited visual field, and contrast or colour vision deficits — affecting use of digital products and benefiting from screen magnification, high-contrast modes, and adjustable text sizing.
Color Blindness
Color blindness (color vision deficiency) is a difference in colour perception affecting approximately 8% of men and 0.5% of women of Northern European descent — most commonly deuteranomaly (reduced green perception) — making colour-only information cues inaccessible.
Deafness
Deafness is profound hearing loss requiring visual alternatives to audio content — captions and transcripts for video, transcripts for audio, sign-language interpretation for live events, and text-based alternatives to voice-only interactions.
Cognitive Disability
Cognitive disability refers to a broad category of conditions affecting cognitive functioning — including dyslexia, attention-deficit disorders, autism, intellectual disability, dementia, and learning disabilities — that influence how people perceive, process, remember, and act on digital content.
Dyslexia
Dyslexia is a learning difference affecting reading fluency and decoding, affecting an estimated 10–15% of the population, that benefits from clear sans-serif typography, sufficient letter and line spacing, and consistent layout — a key target group for cognitive accessibility design.
Photosensitive Epilepsy
Photosensitive epilepsy is a form of epilepsy in which seizures are triggered by visual stimuli — flashing lights, certain patterns, or rapid colour changes — affecting approximately 3% of people with epilepsy and addressed in WCAG 2.3.1 Three Flashes or Below Threshold at Level A.
Motor Impairment
Motor impairment encompasses conditions affecting movement and fine motor control — including cerebral palsy, multiple sclerosis, spinal-cord injury, arthritis, Parkinson's, and tremors — requiring digital products to support keyboard alternatives, larger targets, single-pointer input, and timing flexibility.
Sign Language
Sign language is a visual-gestural language used by deaf communities worldwide — including ASL (American), BSL (British), LSF (French), DGS (German), JSL (Japanese), ISL (Indian) and many others — with WCAG 1.2.6 Sign Language at Level AAA recommending sign-language interpretation for prerecorded synchronised media in healthcare, education, and emergency contexts.
Deafblindness
Deafblindness is the combination of significant hearing loss and significant vision loss — affecting an estimated 0.2–2% of the global population depending on definition — requiring digital products to support refreshable braille output and braille-driven navigation in addition to standard accessibility features.
document
VPAT
A VPAT (Voluntary Product Accessibility Template) is the standard form, originally published by the Information Technology Industry Council (ITI), that vendors complete to disclose conformance of their information and communications technology (ICT) products with Section 508, WCAG, and EN 301 549; a completed VPAT becomes an Accessibility Conformance Report (ACR).
ACR
An ACR (Accessibility Conformance Report) is the completed, filled-in form of a VPAT — a documented statement of how a product conforms to accessibility standards (WCAG, Section 508, EN 301 549) — produced by the product vendor and shared with prospective buyers, particularly in procurement.
Accessibility Statement
An accessibility statement is a public-facing document on a website declaring conformance to one or more accessibility standards, listing known limitations, providing contact channels for accessibility feedback, and outlining the organisation's remediation commitments — required under EAA, WAD, AODA, and the DOJ Title II final rule, and recommended best practice elsewhere.
Overlay Fact Sheet
The Overlay Fact Sheet is a public document at overlayfactsheet.com, authored by Karl Groves and signed by over 900 accessibility professionals (including Adrian Roselli, Léonie Watson, Lainey Feingold), documenting concerns about overlay widgets — their limited efficacy, the privacy implications of third-party DOM manipulation, and the user-facing harms reported by people with disabilities.
GAAD
GAAD (Global Accessibility Awareness Day) is the third Thursday of May each year — co-founded by Jennison Asuncion and Joe Devon — when individuals, companies, and organisations worldwide host events, workshops, and campaigns to raise awareness of digital accessibility.
EAA Accessibility Statement
An EAA accessibility statement is the public-facing document required by Article 13 of the European Accessibility Act, in which each covered service provider declares their conformance status, exceptions claimed (disproportionate burden, fundamental alteration), and complaint-handling channel — with content templated by member-state authorities.
ARIA Authoring Practices Guide
The ARIA Authoring Practices Guide (APG) is a W3C Working Group Note providing detailed implementation patterns for common interactive widgets — accordion, combobox, dialog, menu, tabs, treegrid — with example code, recommended ARIA roles and states, and keyboard interaction guidance.