3.1.3 Unusual Words

Level: AAA | Principle: Understandable | Since: WCAG 2.0 | Automation: Manual

What This Means

A mechanism must be available to identify specific definitions of words or phrases used in an unusual or restricted way, including idioms and jargon. If your content uses technical terminology, industry-specific language, or words with specialized meanings, users must have a way to look up what those words mean.

This applies to idioms (like "kick the bucket"), jargon (like "above the fold" in web design), and any word used in a way that differs from its common dictionary definition. The mechanism can be a glossary, inline definitions, tooltips, definition lists, or links to a glossary page.

People with cognitive disabilities, non-native speakers, and anyone unfamiliar with specialized vocabulary benefit from having definitions readily available without leaving the content.

Who This Affects

Users with cognitive disabilities — specialized language creates barriers to comprehension
Non-native speakers — idioms and jargon are especially difficult for second-language readers
Users unfamiliar with the domain — medical, legal, and technical terms exclude general audiences
Screen reader users — cannot infer meaning from visual context clues that sighted users might use

Common Pitfalls

1. Technical jargon with no definitions

<!-- Bad: jargon with no explanation -->
<p>The API uses RESTful endpoints with JWT authentication and CORS headers.</p>

<!-- Good: terms linked to a glossary -->
<p>
  The <a href="/glossary#api">API</a> uses
  <a href="/glossary#rest">RESTful</a> endpoints with
  <a href="/glossary#jwt">JWT</a> authentication and
  <a href="/glossary#cors">CORS</a> headers.
</p>

2. Idioms used without explanation

<!-- Bad: idiom may confuse non-native speakers -->
<p>This feature is still a moving target.</p>

<!-- Good: definition provided inline -->
<p>
  This feature is still a
  <dfn title="something that is constantly changing and hard to pin down">moving target</dfn>.
</p>

3. No glossary on a technical site

<!-- Good: definition list as a glossary -->
<h2>Glossary</h2>
<dl>
  <dt id="api">API</dt>
  <dd>Application Programming Interface — a set of rules for how software components communicate.</dd>
  <dt id="jwt">JWT</dt>
  <dd>JSON Web Token — a compact, URL-safe token format used for authentication.</dd>
  <dt id="cors">CORS</dt>
  <dd>Cross-Origin Resource Sharing — a browser mechanism that allows controlled access to resources from a different domain.</dd>
</dl>

How to Test

Read through the page content and identify technical terms, jargon, idioms, and words used in specialized or unusual ways.
For each unusual word or phrase, check if a definition mechanism exists: inline <dfn> element with title attribute, a linked glossary entry, a tooltip, or an expandable explanation.
If the site has a glossary page, verify it is linked from the navigation or footer and covers all specialized terms used across the site.
Check that definitions are accurate and understandable to a general audience.
Pass: Every unusual word, idiom, or jargon term has an accessible definition mechanism (inline definition, glossary link, or tooltip).
Fail: Any technical term, idiom, or jargon is used without a definition or glossary entry.

How to Fix

Create a glossary page with definitions for all specialized terms used on the site
Use the <dfn> element with a title attribute for inline definitions of terms on first use
Link technical terms to their glossary entries using standard anchor links
For frequently used jargon, add tooltip definitions that appear on hover and focus
Review content regularly and update the glossary as new terms are introduced