Reference
Digital accessibility glossary
The terms you'll meet in audits, laws and procurement documents, defined in plain English.
- Accessibility Conformance Report (ACR)
- A completed VPAT® describing how a specific product conforms to accessibility standards, criterion by criterion. See VPAT & ACR.
- Accessibility statement
- A public page describing a website's accessibility standard, status, known limitations and how to get help. See how to write one.
- Alt text (alternative text)
- A text description of an image that screen readers read aloud. See the alt text guide.
- ARIA (WAI-ARIA)
- Accessible Rich Internet Applications: HTML attributes that give custom components a role, name and state for assistive technology. Best used only when native HTML can't do the job.
- Artifact (PDF)
- Content in a PDF marked as decorative or repetitive — page numbers, running headers, decorative lines — so screen readers skip it.
- Assistive technology (AT)
- Hardware or software people use to access computers: screen readers, screen magnifiers, refreshable braille displays, switch devices, voice control.
- Auxiliary aids and services
- The ADA's term for ways of making communication effective for people with disabilities, such as captions, braille, accessible electronic formats and screen-reader-compatible websites.
- Captions
- Synchronized text of the dialogue and important sounds in a video, for people who are deaf or hard of hearing. Required for prerecorded video at WCAG Level A and live video at AA.
- Conforming alternate version
- A separate accessible version of content. Under the ADA Title II rule it's allowed only when the primary content can't be made accessible for technical or legal reasons.
- Contrast ratio
- The difference in luminance between text and background, from 1:1 to 21:1. WCAG AA requires 4.5:1 for normal text. See color contrast.
- Demand letter
- A letter from a plaintiff's lawyer alleging accessibility violations and demanding payment and remediation before or instead of a lawsuit. See how to respond.
- EN 301 549
- The European standard for ICT accessibility, used for public procurement and to show conformity with the European Accessibility Act. Its web requirements align with WCAG 2.1 AA.
- European Accessibility Act (EAA)
- EU Directive 2019/882, applying since June 28, 2025 to many products and services sold to EU consumers. See EAA.
- Focus indicator
- The visible outline or highlight showing which element has keyboard focus. Required by WCAG 2.4.7.
- Keyboard trap
- A component that keyboard focus can enter but not leave, a WCAG Level A failure (2.1.2).
- Matterhorn Protocol
- The PDF Association's set of 136 failure conditions for testing PDF/UA conformance, about two-thirds of which can be machine-checked.
- OCR (optical character recognition)
- Software that turns images of text — such as scanned pages — into machine-readable text. See scanned PDFs.
- Overlay
- A third-party script that adds a toolbar and attempts automatic fixes in the browser. It doesn't make websites WCAG-conformant. See overlays.
- PAC (PDF Accessibility Checker)
- A free Windows tool that checks PDFs against PDF/UA and the machine-testable Matterhorn conditions.
- PDF/UA (ISO 14289)
- The international standard for accessible PDF files. See PDF/UA vs WCAG.
- POUR
- WCAG's four principles: Perceivable, Operable, Understandable, Robust.
- Public accommodation
- Under ADA Title III, a private business open to the public in one of twelve categories, such as stores, restaurants, hotels, banks and doctors' offices.
- Public entity
- Under ADA Title II, any state or local government and its departments, agencies, special districts and instrumentalities.
- Reading order
- The sequence in which assistive technology reads content. In PDFs it's set by the tag tree, not the visual layout.
- Remediation
- Fixing accessibility barriers in code, content or documents so they conform to a standard.
- Screen reader
- Software that reads on-screen content aloud or to a braille display and lets users navigate by headings, links, landmarks and form fields. Examples: JAWS, NVDA, VoiceOver, TalkBack.
- Section 504
- Part of the Rehabilitation Act of 1973 prohibiting disability discrimination by recipients of federal funding. See HHS Section 504 rule.
- Section 508
- Part of the Rehabilitation Act requiring federal agencies' ICT to be accessible. See Section 508.
- Success criterion
- A single testable requirement in WCAG, such as 1.4.3 Contrast (Minimum).
- Tags (PDF)
- The hidden structure in a PDF — headings, paragraphs, lists, tables, figures — that assistive technology reads.
- Title II / Title III (ADA)
- Title II covers state and local governments; Title III covers businesses open to the public. See compliance law.
- Undue burden
- A legal defense when an accessibility action would impose significant difficulty or expense, considering all available resources. It must be documented and doesn't remove the duty to provide access another way.
- VPAT®
- Voluntary Product Accessibility Template, published by the Information Technology Industry Council. Completed, it becomes an ACR.
- WCAG
- Web Content Accessibility Guidelines, published by the W3C. Version 2.2 is current; laws mostly cite 2.1 or 2.0 at Level AA. See WCAG 2.2 explained.
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