Glossary
WCAG (Web Content Accessibility Guidelines)
WCAG is the international standard for web accessibility, defining how to make websites usable by people with disabilities — across four principles: perceivable, operable, understandable, robust.
WCAG (Web Content Accessibility Guidelines) is maintained by the W3C and is the international reference standard for web accessibility. The current version is WCAG 2.2 (released 2023); WCAG 3.0 is in working draft as of 2026.
WCAG defines four principles (POUR): Perceivable (content visible/audible to users), Operable (interactive elements usable by everyone), Understandable (clear language and predictable behavior), Robust (compatible with assistive technologies). Each principle breaks down into 13 guidelines and 78+ success criteria.
Compliance levels: A (minimum), AA (mid-level, typical legal requirement), AAA (highest, aspirational). Most legal requirements (ADA in the US, EAA in the EU, AODA in Ontario) reference WCAG 2.1 AA or 2.2 AA. Government sites typically must hit AA; commercial sites face increasing legal pressure to do the same.
Common AA-level requirements: color contrast 4.5:1 for text, alt text for images, keyboard navigation for all interactive elements, focus indicators visible, form labels associated with inputs, no flashing content, language declaration on the html element, semantic landmarks (header / nav / main / footer), heading hierarchy (one h1, h2s in order), error identification on forms.
Why it matters for SEO: many WCAG requirements overlap with SEO best practices (semantic HTML, alt text, descriptive link text, page titles). Sites that meet AA tend to rank better — both because Google's quality signals reward usable sites and because the requirements force good information architecture. Beyond SEO: accessibility is a market-share question (15% of the global population has a disability), a legal-risk question (ADA lawsuits are common), and a basic ethics question.
Example
A site failing WCAG color contrast (gray text on white background, 3.2:1 ratio) excludes ~5% of users with low vision and fails Google's user-experience audits. Bumping the text to a darker gray (4.7:1 ratio) takes 10 minutes and improves both accessibility and dwell-time metrics.