Web Accessibility Glossary

a11y

Accessibility (abbreviation)

a11y is an abbreviation of the word accessibility, where 11 represents the number of letters between 'a' and 'y'. Widely used in the tech community as the hashtag #a11y and in tool and conference names.

ADA

Americans with Disabilities Act

ADA is a US federal law (1990) that prohibits discrimination against people with disabilities. Title II (government entities) and Title III (private sector) extend to websites. In April 2024, the DOJ issued a final rule with specific technical standards (WCAG 2.1 AA) for government sites with a deadline of April 2026.

Alt text

Alternative Text

Alt text is a text description of an image in the alt attribute of the '<img>' tag. Screen readers read alt text to blind users. Decorative images should have an empty alt (alt=""). Informative images need a concise description (up to 125 characters). Missing alt is one of the most common errors: 54.5% of images lack alt (WebAIM Million 2025).

ARIA

Accessible Rich Internet Applications

ARIA is a W3C specification that defines a set of HTML attributes for improving the accessibility of dynamic web content. It includes roles (role), states (aria-expanded, aria-hidden), and properties (aria-label, aria-describedby). First rule of ARIA: if a native HTML element has the needed semantics, use it instead of ARIA.

Assistive Technology

Assistive Technology (AT)

Assistive technologies are devices and software that help people with disabilities use computers and the internet. Examples include screen readers (NVDA, JAWS, VoiceOver), screen magnifiers (ZoomText), alternative keyboards, eye-tracking, and switch devices.

Accessibility Overlay

Overlay (accessibility overlay)

An overlay is a JavaScript widget that adds a settings panel on top of a site (fonts, contrast, cursor). It does not modify the actual HTML code. The National Federation of the Blind and 700+ specialists (overlayfactsheet.com) state that overlays do not provide real WCAG compliance. The FTC fined AccessiBe $1M in 2025.

Accessibility Statement

An accessibility statement is a public document on a website that describes the level of accessibility, known limitations, contact information for reporting issues, and planned improvements. Required by the EAA in the EU and recommended by W3C WAI.

CLS

Cumulative Layout Shift

CLS is a Core Web Vitals metric from Google that measures the visual stability of a page. A good score is below 0.1. Elements that shift after loading (images without dimensions, dynamic content, fonts without font-display: swap) increase CLS and hurt SEO rankings.

Color Contrast

Color Contrast Ratio

Color contrast is the numerical ratio of luminance between text and background. WCAG 2.1 Level AA requires a minimum of 4.5:1 for normal text and 3:1 for large text (>18pt or >14pt bold). Level AAA: 7:1 and 4.5:1. Low contrast is the most common error: 81% of sites have this issue (WebAIM).

Cognitive Accessibility

Cognitive accessibility is design for people with cognitive impairments: dyslexia, ADHD, autism, memory problems. It includes clear language, consistent navigation, minimal distractions, sufficient time for actions, and clear instructions. WCAG 2.2 added criteria for this group.

CAPTCHA

Completely Automated Public Turing test

CAPTCHA is a test to distinguish humans from bots. Visual CAPTCHAs (distorted text, image selection) are a barrier for blind users and those with cognitive impairments. WCAG requires an alternative way to pass. Recommended: reCAPTCHA v3 (invisible) or hCaptcha with an audio alternative.

DSTU EN 301 549

DSTU EN 301 549:2022

DSTU EN 301 549:2022 is the Ukrainian national standard for ICT product accessibility, identical to the European EN 301 549 v3.2.1. It includes requirements for websites (based on WCAG 2.1 Level AA), mobile applications, documents, and self-service terminals.

Digital Accessibility

Digital accessibility ensures that digital products (websites, apps, documents, videos) can be used by people with disabilities. It is broader than web accessibility and includes mobile apps, PDF documents, e-books, and video with captions.

DOM

Document Object Model

The DOM is a tree-like structure of an HTML page that the browser creates for rendering and manipulating content. The Accessibility Tree is a separate version of the DOM used by screen readers to vocalize the page. A correct DOM leads to a correct Accessibility Tree.

EAA

European Accessibility Act

The EAA (EU Directive 2019/882) is an EU law requiring accessibility of digital products and services. It took effect on June 28, 2025, in all 27 EU countries. It covers e-commerce, banking, telecom, and transport. Technical standard: EN 301 549 (based on WCAG 2.1 Level AA). Penalties are determined at the national level.

EN 301 549

Harmonised European Standard for ICT Accessibility

EN 301 549 is a European standard for ICT accessibility from ETSI/CEN/CENELEC. Version 3.2.1 (2021) is the harmonised standard for the EAA. For web: based on WCAG 2.1 Level AA. Also covers mobile apps, documents, software, hardware, and self-service terminals.

E-E-A-T

Experience, Expertise, Authoritativeness, Trustworthiness

E-E-A-T is Google's framework for evaluating content quality. Experience: demonstrated experience. Expertise: author qualifications. Authoritativeness: domain authority. Trustworthiness: credibility. Important for SEO and AI citations. Not a direct ranking factor, but influences through content quality.

Focus Indicator

Focus Indicator / Focus Ring

A focus indicator is a visible outline around an interactive element (link, button, field) when it receives keyboard focus. WCAG 2.4.7 (AA) requires a visible focus. WCAG 2.2 added 2.4.11 (Focus Not Obscured) and 2.4.13 (Focus Appearance) with minimum contrast and size requirements.

Focus Trap

Focus Trap / Keyboard Trap

A focus trap is a situation where a keyboard user cannot leave an element (modal, widget) using Tab or Escape. WCAG 2.1.2 (A) prohibits focus traps. Exception: modals SHOULD keep focus inside, but MUST have a way to close (Escape).

Form Accessibility

Form accessibility ensures that forms can be filled out by people with disabilities. Each field needs a label (programmatically linked via for/id or aria-label). Errors must be clearly described and linked to the field. Required fields should not be indicated by color alone. The form must work with a keyboard.

Heading Hierarchy

Heading hierarchy is the logical structure of h1-h6 on a page. One h1 per page (title). h2 for main sections. h3 for subsections. Do not skip levels (h1 to h3 without h2 is an error). Screen readers use headings for navigation. 42.7% of pages have skipped heading levels (WebAIM).

High Contrast

High Contrast Mode

High contrast is a display mode with increased contrast between text and background. Windows High Contrast Mode (forced-colors) changes system colors. A site should function correctly in this mode. CSS media query: @media (forced-colors: active).

Keyboard Navigation

Keyboard navigation is the ability to fully operate a site without a mouse, using only a keyboard. Tab moves between elements, Enter activates, Escape closes, arrows navigate within menus/sliders. WCAG 2.1.1 (A) requires all functionality to be accessible via keyboard.

Landmark

ARIA Landmark / HTML Landmark

A landmark is a semantic region of a page that helps screen reader navigation. HTML5 elements: '<header>', '<nav>', '<main>', '<aside>', '<footer>'. ARIA roles: role="banner", role="navigation", role="main", role="complementary", role="contentinfo". Use HTML5 elements over ARIA roles where possible.

Live Region

ARIA Live Region

A live region is an area of a page whose changes are automatically announced by screen readers. aria-live="polite" announces when convenient. aria-live="assertive" announces immediately (for errors, alerts). role="status" and role="alert" are built-in live regions.

Overlay

Accessibility Overlay Widget

An overlay is a JavaScript accessibility widget that applies changes on top of a page without modifying the actual HTML. Products: AccessiBe, UserWay, EqualWeb. Criticism: overlayfactsheet.com (700+ signatories), NFB statement, FTC AccessiBe $1M fine. Alternative: DNS-proxy approach (InclusiveWeb) that actually fixes HTML before delivery to the visitor.

POUR

Perceivable, Operable, Understandable, Robust

POUR represents the four principles of WCAG. Perceivable: content is available to all senses. Operable: the interface works in different ways. Understandable: content and navigation are clear. Robust: works with various technologies, including assistive ones.

Role (ARIA)

ARIA Role

An ARIA Role is an attribute that defines the semantic role of an element for assistive technologies. Types: widget roles (button, checkbox, tab), document roles (article, heading), landmark roles (navigation, main), live region roles (alert, status). HTML5 elements have built-in roles: '<button>' = role="button".

Screen Reader

A screen reader is software that vocalizes screen content for blind and visually impaired users. Popular ones: NVDA (Windows, free), JAWS (Windows, commercial), VoiceOver (macOS/iOS, built-in), TalkBack (Android, built-in). 53.7% of screen reader users use NVDA (WebAIM Survey 2024).

Section 508

Section 508 of the Rehabilitation Act

Section 508 is a US law requiring ICT accessibility for federal agencies. Updated in 2017 to reference WCAG 2.0 Level AA. It covers websites, documents, software, and hardware developed or procured by the federal government.

Semantic HTML

Semantic HTML means using HTML elements for their intended purpose: '<button>' for buttons (not '<div onclick>'), '<nav>' for navigation, '<h1>'-'<h6>' for headings, '<table>' for tabular data. Screen readers understand the semantics of native elements. Div soup (everything built with divs) is the most common architectural accessibility error.

Shadow DOM

Shadow DOM is a Web Components technology that isolates a widget's DOM and styles from the main page. The InclusiveWeb accessibility panel uses Shadow DOM: panel styles do not conflict with site styles, and vice versa. This ensures the widget works correctly on any site.

Skip Link

Skip Navigation Link

A skip link is a hidden link at the top of a page that appears when Tab is pressed, allowing users to jump directly to the main content, bypassing the navigation. WCAG 2.4.1 (A) requires a mechanism to bypass repeated blocks. Implementation: '<a href="#main" class="skip-link">'.

Tab Order

Tab order is the sequence in which elements receive focus when Tab is pressed. It should match the visual content order (left to right, top to bottom). WCAG 2.4.3 (A). tabindex="0" adds to the natural order. tabindex="-1" allows programmatic focus. tabindex > 0 is an anti-pattern; avoid it.

Text Alternatives

Text alternatives are textual equivalents of non-text content. WCAG 1.1.1 (A) requires alternatives for: images (alt), video (captions, audio description), audio (transcription), icons (aria-label), CAPTCHA (audio alternative). This is the most common category of accessibility errors.

WAI

Web Accessibility Initiative

WAI is a W3C (World Wide Web Consortium) initiative that develops web accessibility standards and guidelines. Main products: WCAG (content standard), ARIA (interactivity standard), ATAG (authoring tools standard), UAAG (user agent standard).

WAVE

Web Accessibility Evaluation Tool

WAVE is a free accessibility testing tool from WebAIM. Available as a web service (wave.webaim.org), Chrome/Firefox extension, and API. It shows errors, warnings, and structural elements directly on the page. It does not replace a full audit: automated tools find only 30-57% of issues.

WCAG

Web Content Accessibility Guidelines

WCAG is the international web content accessibility standard from W3C. It defines technical criteria for making sites accessible to people with disabilities. Current versions: WCAG 2.1 (2018, 78 criteria) and WCAG 2.2 (2023, 87 criteria). Levels: A, AA (recommended), AAA. The basis for EAA, ADA, and DSTU EN 301 549.

WCAG 2.1

Web Content Accessibility Guidelines 2.1

WCAG 2.1 (June 2018) extended WCAG 2.0 with 17 new criteria for mobile accessibility, low vision, and cognitive impairments. 78 success criteria. The base standard for EN 301 549 and EAA. Still the most commonly required version in legislation (ADA, DSTU).

WCAG 2.2

Web Content Accessibility Guidelines 2.2

WCAG 2.2 (October 2023) is the latest update. 87 criteria (+9 new, -1 removed). New criteria: Focus Not Obscured, Focus Appearance, Dragging Movements, Target Size Minimum, Accessible Authentication, Consistent Help, Redundant Entry. Recommended standard for new projects.

WCAG Levels

WCAG Conformance Levels (A, AA, AAA)

WCAG defines three levels: Level A (30 criteria in 2.2) is minimum accessibility; without it the site is practically unusable. Level AA (24 criteria) is the recommended standard, required by EAA, ADA, and DSTU. Level AAA (33 criteria) is maximum accessibility, rarely required in full.

Web Accessibility

Web accessibility is the practice of building websites that can be used by all people, regardless of disability, age, or technology. It includes screen reader compatibility, keyboard navigation, sufficient contrast, video captions, and a clear structure. 96.3% of sites have accessibility errors (WebAIM Million 2025).