:Update: Not any more it doesn't - it just has a brief summary instead.
Japanese. Usually means "lewd", "suggestive", "sexual", or something of the sort. Literally is the letter "H", the first letter of "hentai", which means "pervert" or "perverted".
Used of:
A person, as an adjective or a general maddened cry of rage... often said to a male anime character, by a female one to whom he's just said or done something suggestive.
An anime (or other piece of fiction or entertainment) to indicate it contains scenes of this kind.
A camera angle, a facial expression, just about anything.
[This page] has a couple of entertaining rants about the difference between "ecchi" (or "H") and "hentai", and the ways they're often used incorrectly by Western fans.
Update: Not any more it doesn't - it just has a brief summary instead.