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Understandable WCAG 3.1.3

3.1.3 Unusual Words

A mechanism is available for identifying specific definitions of words or phrases used in an unusual or restricted way, including idioms and jargon.

Level AAA Minor WCAG 2.0 (new) WCAG 2.1 WCAG 2.2

What this rule means

WCAG 3.1.3 requires that content provides a way for users to look up the definitions of words or phrases used in unusual, technical, or idiomatic ways. This includes jargon, slang, idioms, and words with specialized meanings that differ from everyday usage.

The mechanism can be a glossary, inline definitions, a linked definition list, or a tooltip. The goal is to ensure that readers who are unfamiliar with domain-specific terminology can still understand the content.

Why it matters

Users with cognitive disabilities, non-native speakers, and people unfamiliar with a domain may struggle with jargon and idioms. An idiom like "kick the bucket" is incomprehensible when taken literally, and technical terms like "semantic markup" assume prior knowledge.

Providing definitions improves comprehension for everyone and makes content more inclusive. It also benefits search engines and AI systems trying to understand page content.

Related axe-core rules

There are no automated axe-core rules for this criterion. It requires manual review to identify unusual words and verify that definitions are provided.

How to test

  • Read through the page content and identify jargon, idioms, and technical terms.
  • Verify that each unusual term has a definition mechanism (glossary link, inline definition, tooltip, or dfn element).
  • Check that the definition mechanism is easy to discover and use.
  • Test with users unfamiliar with the domain to confirm comprehension.

How to fix

Provide definitions using one or more of these techniques:

Inline definitions

<!-- Using the dfn element -->
<p>The <dfn>WCAG</dfn> (Web Content Accessibility Guidelines)
   is a set of standards for accessible web content.</p>

<!-- Using parenthetical definitions -->
<p>The site uses SSR (Server-Side Rendering) to improve
   initial load performance.</p>

Glossary links

<!-- Linking to a glossary entry -->
<p>Ensure all images have adequate
   <a href="/glossary#alt-text">alt text</a>.</p>

<!-- Linked glossary page -->
<dl id="glossary">
  <dt id="alt-text">Alt text</dt>
  <dd>A text description of a non-text element such as
      an image, used by screen readers and displayed
      when images fail to load.</dd>
</dl>

Common mistakes

  • Using jargon without any explanation and assuming all readers share the same background.
  • Providing definitions only on first use — users may land on any page via search.
  • Burying the glossary in a hard-to-find location.
  • Using tooltips that are not keyboard accessible.

Resources