an HTML tag, used in the context of description lists, that's to say within the DL tag.
Defined in HTML 2.0 as
<!ELEMENT DT - O (%text)*>
which means (in SGML
verily, I can contain %text, any amount of it from zero to infinity, and I need no closing tag. Which does not mean that I am an empty tag, mind you.
Expressive language, isn't it ? %text, which is not a tag is defined as "#PCDATA | A | IMG | BR | %phrase | %font". To make matters clearer, anything that can go inside a P tag can go inside a DT tag.
Which means more or less anything but tables, headers, paragraphs (in HTML 3.2 this is explained as text level elements, as opposed to block level elements).
DD is much more permissive as far as its content is concerned.
the definition looks different
<!ELEMENT DT - O (%inline;)* -- definition term -->
but it does not really mean anything different, as the spec makes painfully clear by defining %inline through various and tasty entities that basically boil down to text level elements.