Accessibility & Compliance Glossary
Digital accessibility comes with a dense vocabulary of standards, laws, and acronyms. This glossary defines the terms clearly and accurately, with sources you can check, so you can tell a VPAT from an ACR, a Level A criterion from Level AA, and a genuine fix from an overlay's marketing claim. Each definition links to the tools and guides that put it to work.
Standards & Guidelines
WCAG (Web Content Accessibility Guidelines)
WCAG is the W3C's technical standard for making web content accessible, and the benchmark most accessibility laws point to.
Read definitionWCAG Conformance Levels (A, AA, AAA)
WCAG sorts its success criteria into three conformance levels, A, AA, and AAA, with Level AA being the standard target for legal compliance.
Read definitionPOUR Principles
POUR is the acronym for WCAG's four foundational principles: content must be Perceivable, Operable, Understandable, and Robust.
Read definitionEN 301 549
EN 301 549 is the European standard for ICT accessibility, used across EU public procurement and referenced by the European Accessibility Act.
Read definitionPDF/UA (ISO 14289)
PDF/UA is the ISO standard (14289) that defines how to make PDF files accessible, complementing WCAG with PDF-specific technical requirements.
Read definitionLaws & Regulations
Section 508
Section 508 of the Rehabilitation Act requires U.S. federal agencies to make their electronic and information technology accessible, using WCAG 2.0 Level AA as the technical standard.
Read definitionADA (as it applies to websites)
The Americans with Disabilities Act is a U.S. civil-rights law that courts and regulators increasingly apply to websites, with WCAG Level AA treated as the practical standard.
Read definitionEuropean Accessibility Act (EAA)
The European Accessibility Act (Directive (EU) 2019/882) requires a wide range of private-sector products and services to be accessible across the EU, with obligations applying from June 28, 2025.
Read definitionDocumentation & Procurement
VPAT (Voluntary Product Accessibility Template)
A VPAT is a standardized template, published by ITI, that vendors use to document how their product conforms to accessibility standards.
Read definitionACR (Accessibility Conformance Report)
An Accessibility Conformance Report is the completed, filled-in VPAT that documents a product's actual conformance findings.
Read definitionVPAT vs ACR
The VPAT is the blank template; the ACR is the completed report you produce by filling it in, so every ACR starts life as a VPAT.
Read definitionTesting & Tools
axe-core / Automated Testing
axe-core is a widely used open-source accessibility testing engine; like all automated testing, it reliably catches the machine-detectable subset of WCAG issues, roughly 30-40 percent.
Read definitionAccessibility Overlay
An accessibility overlay is a third-party script that claims to automatically fix a site's accessibility; the accessibility community broadly warns that overlays cannot deliver genuine compliance.
Read definitionTechnical Concepts
WAI-ARIA
WAI-ARIA is a W3C specification that adds roles, states, and properties to markup so custom interface components can be understood by assistive technologies.
Read definitionAlt Text
Alt text is the text alternative for an image, required by WCAG success criterion 1.1.1 so that people who cannot see the image still receive its information.
Read definitionFrom definitions to your own results
Knowing the terms is the first step. Run a free scan of your site against WCAG 2.2 Level AA to see which of these concepts apply to your pages right now, with a score, a severity breakdown, and fix suggestions.
Related Resources
Accessibility Compliance Hub
How ADA, WCAG 2.2, Section 508, and the European Accessibility Act apply, broken down by industry.
Compare Accessibility Tools
See how CompliaScan compares to other accessibility scanners and overlay widgets, side by side.
Free Accessibility Tools
Color contrast checker, WCAG 2.2 checklist, alt text checker, and accessibility statement generator.
Accessibility Guides
In-depth guides on WCAG 2.2, Section 508, ADA website compliance, and accessibility audits.
VPAT Starter Generator
Turn scan results into a draft VPAT/ACR starting point for federal and state procurement.
Free WCAG Checker
Scan any page against WCAG 2.2 Level AA and get fix suggestions in seconds.