Lemon

A Lemon is smutfic, a fanfiction with explicit sexual content. This can range from plot-what-plot boinkfests with no justification or explanations to exquisitely plotted and crafted stories that just happen to follow their participants into the bedroom (and through the subsequent action therein) on a regular basis. Once a common term, it's now less frequently seen, though by no means extinct.
Lemons tend to have explicit sexual content, if not actual sex.
The term derives from the idea that like a lemon, sexuality looks beautiful and alluring, but when you experience it more directly, it's bitter and sour.
While some Lemons do tend to have the occasional original character or Mary Sue, they generally tend to feature canon characters.
Can be used as a noun and an adjective interchangeably: "It's a lemon story" and "it's a lemon" are functionally equivalent. Surprisingly, the term is not automatically synonymous with "bad" (although that, as the saying goes, is often the way to bet).
Category: Terminology