Fiction written by people who enjoy a film or particularly a television show, using the characters and situations developed in the film or show and developing new plots in which to use these characters.
Fan fiction has come to the fore especially since the rise of the Internet, where it flourishes despite the possibility that it may infringe the copyright of the film or tv show on which it is based. Thus far, the major studios have generally tolerated fan fiction since it has not assumed commercial importance.
An historical version of fanfiction, "Slash" has been around since the 1960s. Named for stories featuring two characters interacting (often sexually) as in Kirk/Spock, these stories were often passed around in feminist fanzines. Nowadays the largest form of fanfic is based on Japanese anime/manga series, followed by American cartoon series and science fiction serials.