Fan fiction featuring homosexual acts, relationships, or desires, generally as a major component of the plot. Slash usually involves two or more male characters as the romantic leads, although stories featuring multiple partners of mixed genders are usually categorized as slash. When stories featuring female same-sex relationships began to appear, there was some debate among slashers, but femmeslash is now widely recognized as a subgenre of slash. There has been some move to include heterosexual non-canonical pairings under the rubric slash, but this is not widely accepted.

Slash as a recognizable genre began in the late 1960's with the development of K/S, stories depicting a romantic love between the characters Kirk and Spock from Star Trek: The Original Series. This was different from earlier stories which had depicted male bonding and platonic love between male characters on television.

The name slash derives from the virgule used to separate K/S, and differentiate it from friendship stories, designated K&S.

Slash makes explicit the homoerotic subtext prevalent in many tv shows. Classic pairings for slashing include Starsky/Hutch from Starsky and Hutch, Han/Luke and from Star Wars. More modern objects include Qui-Gon/Obi Wan from The Phantom Menace, Clark/Lex from Smallville, and Blair Sandburg/Jim Ellison from The Sentinel.

Slash usually draws its subjects from tv, particularly cop shows and sci fi. However, movies, books ranging from the work of Anne Rice to the Bible, and the plays of Shakespeare have served as fodder. Of late, and controversially, RPF and RPS or real person fiction/slash, have been gaining in popularity, focusing largely on pop musicians such as the members of *NSYNC, Britney Spears, and Eminem, as well as actors (e.g., the cast of The Lord of the Rings as directed by Peter Jackson), and professional athletes, although there are rumors that people were writing similar stories about Led Zeppelin and The Beatles as drawerfic in the 1970's and before.