facts which are generally accepted within a genre's fanfiction community, but never appear in official continuity. Ex. Vegeta's full name being "Vegeta Briefs" is fanon.
Different from canon, fanon has never appeared in an actual episode. It consists of those things that have popped up in fanfiction so frequently that many people accept them as fact. Sometimes it becomes difficult to separate fanon from canon.
a new, mostly online term, for ideas not based in canon that are accepted in fanfic as fact (e.g. that Starsky's dad was a cop or that Hutch has a sister)
common situations occuring in fan fiction of a particular fandom. Example: Hakkai and Goyjo being more than roomates in fan fiction based on the anime and manga Saiyuki.
as distinct from 'canon'. stuff that didn't actually happen in canon but that fanfic authors seem to believe anyway (angel sired spike, the padawan braid-cutting ceremony). sometimes the boundary between canon and fanon is a miles-wide demilitarized zone, sometimes it's a disputed border that could flare up into conflict at any moment. sometimes my analogies make no sense.
facts that are extrapolated from the source material in fanfics, orjust plain made up. As much as we like to believe it, the HP characters being gay is fanon
Information that was never stated in the show's canon, but has become accepted as fact by fans.
general] That which is conventional in fanfic, despite a lack of support in the source material. Outstanding Mizzy examples are the use of "Marcelin" as Enjolras's given name, or Grantaire's calling Enjolras "Apollo". Should never be confused with canon. Marcelin Enjolras and Other Pitfalls
Fan made "truths" derived usually from fan work (like fanfics or doujinshi) which other fans take as canon.
Information or characterization that has never been confirmed in canon but is accepted as such by fans. In canon Justin made jambalaya once for Brian, but fanon paints Justin as the primary cook in the household. Brian is on a strict diet is another bit of fanon. The mere fact that he eats at a DINER (and a Pittsburgh diner at that) means that he's not that fastidious about his meals, and while it may be canon that he "doesn't do carbs or fat after 7," we've seen him binge on junk food with Michael.
Works of fan fiction which have become pseudo canon to their fans i.e. the stories by Thing1, Hermione Queen of the Witches by Arabella, and of course, the Uberfic.
"Fanon" is a detail about a particular show or character that was created by a fan but has now been generally borrowed/copied/accepted as canon by many other writers. For instance, in a story about THE SENTINEL, Susan Williams had Blair borrowing Jim's Cascade PD sweatshirt, and now sweatshirt-borrowing is often portrayed as Blair's habit in other stories by other writers, making it fanon. See also: CANON.
Concepts, ideas or beliefs about the series that have never been explicitly told to fans by the producer/writer, but have become so commonly used in the fandom that they are taken as fact.
Fanon is a fact or ongoing situation related to a television program, book, movie, or video game that has been used so much by fan writers or among the fandom that it has been more or less established as having happened in the fictional world, but which does not appear in any official work from the original authors, scriptwriters or producers. The term is a play on the word canon.