Do you know the <dfn> tag and what it is used for?

Yes, I know.

The <dfn> (Definition) tag is used to denote a term that is defined within the surrounding content.

Its main purpose is to semantically highlight the defined term so that search engines, screen readers, and other tools can identify it.

Example of usage:

<p>
  In web semantics, <dfn>HTML</dfn> is a hypertext markup language.
</p>

In this case, the <dfn> tag highlights the term "HTML," which is defined in the sentence. If there is an <abbr> element next to <dfn>, then <dfn> will refer to the full form of the abbreviation:

<p>
  In web semantics, <dfn><abbr title="HyperText Markup Language">HTML</abbr></dfn> is a hypertext markup language.
</p>

The appearance of the <dfn> element by default often does not differ from regular text, but it can be styled using CSS.