The Definition List element represents a list of terms and
corresponding definitions. Typical formatting of a definition list is
flush left for the term (DT) with the definition (DD) indented on a
separate line (block formatted.) An alternate method of display is to have
the DD indented following the DT item on the same line to more strongly
associate the term/definition relationship.
The contents of this list structure is a sequence of DT and DD terms (this
is the only list structure in which the DT and DD elements are allowed to appear,
and they are usually found in pairs.) Multiple DTs may be grouped with a
single DD, but should not contain multiple consecutive DD elements. As with
other list elements, the closing </dt> and
</dd> tags are optional, as they are
implied by the subsequent list items or end
</dl> tags.
Despite the above caveat to not have multiple consecutive DD elements,
most browsers have no problem with it.
One of the most common usages for this list structure is solely to achieve
indentation capability with the DD element [this document is an example.]
Useless Trivia: There appears to be some
confusion as to what DD stands for mnemonically, even in the official
W3C documentation. I have heard all of these used: "Definition
Definition", "Definition Discussion" and "Definition
Description". It probably doesn't matter which term is used, as
long as both parties can agree to the subject being discussed.