In the world of fandom (check out fan fiction, fanfiction, fanfic(s), or fic(s)), a lemon is a story which consists of sexually explicit themes and situations.

SYNONYMS:

Limes: More romantic and cuddly than sexual, with some fooling around and kissing.

PWP: Stands for “Porn Without Plot” or “Plot? What Plot?” Much more hardcore and to the point than lemons. As the name suggests, it’s all about sex, and is completely absent of any storyline or plot that would take place in a lemon or lime.

You can google Harry Potter lemons (just about any popular work of fiction for teens will do) or google anime lemons.

A person with an outwardly dominant, masculine, or aggressive personality, but who also enthusiastically takes on the submissive or "bottom" role in the bedroom.

Sour-tasting egg laid by citrus duck

I don't know what everyone else is talkin about. A Lemon's a fruit. A little yellow fruit.

a fruit that’s the same color as it’s name

Sour shit life can give you, and with which you can do whatever the hell you want.

An anime/manga or (anime/manga) based fan-work that depicts sexual acts.

Often shortened to simply "Lemon", the term is actually derived from a hentai anime in 1984, "Cream Lemon", which told a story about a girl called Ami and her relationships.

Since then "Lemon" has been used to refer to all sexually-oriented fanworks, in particular fan-fiction.