from the Japanese verb 'ukeru' (receive) it's used in anime/manga and fanfiction for the "bottom" or "passive" in a wordyaoi/word/wordshounen-ai/word (male/male) relationship.
Generally the shorter, cuter, sweeter of the two... generally.
See wordseme/word for more info.

The male in a yaoi relationship that's usually the bottom, and recieves it instead of giving it.
Rei Ryugazaki.

partner on bottom, submissive one in relationship , usually younger and less experienced the the seme

The Japanese term for the partner on the bottom. Used in conjunction with seme and yaoi.

Often referring to yaoi manga, ukes are usually the bottom ones. Opposite of semes, ukes are usually cute, has less experience with sex, kind, those kinds of things.

The person on "bottom" or the submissive person during intercourse. Contrary to popular belief, this word is not always associated with sonen-ai or the likes thereof.

Ukes are Ukueles... people who think otherwise are wrong