Lemon is a term used in reference to anime and manga, especially fanfiction, to describe material with explicit sexual content, such as hentai, yaoi, and yuri.
Some have elaborated this into a string of different terms involving citrus to describe the "rating" of a particular piece; a hint of citrus indicates subtle innuendo, etc. The most common derivative is lime, which denotes sexual content that is not quite explicit. The use of this term (and its derivatives) is increasing in non-anime fanfiction communities.
The term is derived from the anime video series Cream Lemon, a historically important sexually explicit anime (though not quite the first).
