Slash fiction is a genre of fan fiction which focuses on relationships, ranging from relatively tame slash fiction in which characters hold hands and kiss to extremely explicit fiction which leaves little to the imagination. Like other forms of fan fiction, it uses characters and concepts from books, films, and television shows, although it may be wildly divergent from the original source material. Many fan fiction sites have separate areas for slash fiction, which is typically rated so that readers can know what kind of material to expect.

Because slash fiction uses characters created by someone else, it is subject to the same legal issues that fan fiction struggles with. Some authors are very supportive of fan fiction, since they greatly enjoy seeing what other people do with their characters. Others, however, are opposed to fan fiction and especially slash fiction, because they believe that it corrupts their original intent or work. This is particularly the case with explicit slash fiction, which may include controversial topics such as non-consensual sexuality, BDSM, or underage sexuality.

The origins of slash fiction stretch back to at least the 1970s, when Star Trek fans first began writing erotic fiction about the characters in the television series. Much of this fiction was homoerotic in nature, and it often featured the pairing of Captain Kirk and Spock, usually abbreviated as Kirk/Spock. For quite some time, people thought of slash fiction as specifically homosexual, although heterosexual, lesbian, intersex, and polyamorous relationships also appear in slash fiction. Lesbian slash fiction is sometimes called “femmeslash.”

The “slash” in slash fiction refers to the forward slash used to identify a relationship between two characters, such as Ron/Hermione, in a popular so-called canon pairing which often appears in Harry Potter slash fiction. “Canon” refers to fiction which closely follows the facts established in the original series, while non-canon fiction introduces unlikely concepts, characters, or situations. Some slash fiction authors try to stick with canon, while others prefer to be more adventurous.

Many people think of slash fiction as a harmless diversion, although it may put beloved or familiar characters in shocking situations. Others are uncomfortable with some of the darker aspects of slash fiction, especially slash fiction which glorifies acts of questionable legality, such as underage sex. Some people call slash fiction with underage sex “chanslash,” in a reference to “chan,” a Japanese diminutive. Some authors who are supportive of fan fiction do draw the line at chanslash, because it conflicts with their personal morals.