Fan fiction, also known as fanfiction, fanfic or FF, is new fiction by fans of characters or settings of original works of fiction created without the permission or authorization of the original creator. Fan fiction is rarely published in conventional book format, except in collections of fan fiction, and is most commonly distributed online or at fan conventions. Popular genres of fan fiction include fetish or sexual fiction, alternate universe fiction, comic book characters, television series continuation, crossover fiction or simply romantic fan fiction, pairing characters in a more romantic context but not reaching into explicit prose.
Prior to the digital era, elements of other author's works might be incorporated into a work as a parody or homage to the original author; as with today's fan fiction, these incorporated elements would not be considered canon (officially valid material in a fictional universe or setting of a story), but these works were commercial. Today's fan fiction is mostly non commercial and serves to continue the enjoyment of characters of existing works. Fan fiction is not canonical; therefore, events that happen in the context of a fan fiction story are not considered "real" to the original stories.
While some of the work is purely sexual (kink or fetish that focuses on sexual activities outside of mainstream discussion or "slash" which puts traditional heterosexual characters like Star Trek's Kirk and Spock into a same-sex relationship), much of the work is about expanding the adventures of discontinued television, movie or book series. There are dozens of full-length fan fiction Harry Potter books exploring events in-between the book settings and after the series' end in so-called alternate universes. This allows the new author to resurrect a deceased character, change unpopular plot points or even alter the course of the story completely. These stories are often built on by multiple fan fiction authors, sometimes maintaining anonymity.
Comic book characters are popular showcases for talented artists and writers on the Internet, especially with the advent of so many successful comic book conventions. Supposedly leaked plots of upcoming superhero films are often fan fiction pieces. Cancelled television series sometimes inspire fans to produce proper ends for unresolved cliff-hangers or continue the series on a regular basis. Crossover fiction incorporates characters or settings from multiple fictional universes into a single story. Romantic pairings of characters do not have to be the pornographic or explicitly sexual variety. Fan fiction authors sometimes pair audience favorites like Kate and Jack of Lost in their works.
Fan fiction's legality is a still debated issue. In the United States it is considered a derivative work and is not covered under the fair use exception. While some prominent writers have encouraged the creativity of the readers of their works, others are aggressive defenders of their copyrights and work to fight any attempt to publish (even for free and online) any fan fiction featuring their characters.