The HTML <dfn> element (or HTML Definition Element) represents the defining instance of a term.

HTML5 Usage Notes:
The <dfn> element marks the term being defined; the definition of the term should be given by the surrounding <p>, <section> or definition list group (usually a <dt>, <dd> pair).
The exact value of the term being defined is determined by the following rules:
1. If the <dfn> element has a title attribute, then the term is the value of that attribute.
2. Else, if it contains only an <abbr> element with a title attribute, then the term is the value of that attribute.
3. Otherwise, the text content of the <dfn> element is the term being defined.

Content categories:
Flow content, phrasing content, palpable content.

Permitted content:
Phrasing content, but no <dfn> element must be a descendant.

Tag omission:
None, both the starting and ending tag are mandatory.

Permitted parent elements:
Any element that accepts phrasing content.

DOM interface:
HTMLElement

Notes:
In HTML5, the title attribute has special meaning, as noted above.
