List in which each item consists of two parts: 1) a word, phrase, term, graphic, chemical structure, or equation, that is paired with 2) one or more descriptions, discussions, explanations, or definitions of it.
The following, in order:
<term-head> Definition List: Term Head, zero or one
<def-head> Definition List: Definition Head, zero or one
<def-item> Definition List: Definition Item, one or more