<dfn>
The defining instance of a term — the one place where the term is explained.
Baseline: Widely available · Inline text semantics
When to use it
On a term's first, defining mention; give it an id so other pages and passages can link to the definition.
When not to
Only the defining occurrence gets dfn — later mentions are plain text or links back to it.
Key attributes
id- cross-reference anchor
title- the term being defined, if the content isn't it
Example
A landmark is a region screen readers can jump to directly.
<p>A <dfn id='def-landmark'>landmark</dfn> is a region screen readers can jump to directly.</p>