Slash fiction is a genre of fan fiction that depicts characters in same-sex romantic or sexual relationships. The term is believed to have originated in the 1970s with stories featuring the "K/S" tag, denoting the characters of James T. Kirk and Mr. Spock in such a relationship.
Slash stories tend to take a view alternate to the canonical orientation (whether explicit or implicit) of these characters, though stories featuring canonical homosexual relationships are often labeled slash as well. Likewise, slash fiction is not inherently erotic in nature, and spans all ratings, from all-ages to NC-17.
Slash fiction involving female characters is also referred to as femslash. Slash pairings are often abbreviated; for example, a slash fiction between James T. Kirk and Spock is known as Kirk/Spock, abbreviated as K/S.