Canon (in the context of fandom) is a source, or sources, considered authoritative by the fannish community. In other words, canon is what fans agree "actually" happened in a film, television show, novel, comic book, or concert tour. The term derives from the theological concept of canon, the foundational texts of a religion. Specific sources considered canon may vary even within a specific fandom.

Official vs. Canonical

In some cases, a fandom may embrace one work by an author, and yet reject a closely related work as "not canon." An author's works may be considered canon, while statements by the author are often considered to be merely opinion.

Prop canon is related to physical objects shown in a movie or a TV show, for example college degrees, driver's licenses, etc. Lacking conflicting evidence, prop canon is considered a reasonably canonical source, but occasionally dialog, or later show development may cancel it out. For example, in Stargate SG-1, Jack O'Neill had different birthdates depending on which driver's license was shown, while Rodney McKay on Stargate Atlantis has a certificate on his wall that gives his name as 'Rodney Ingram McKay' which was later contradicted in the episode McKay and Mrs. Miller when his sister said his full name was Meredith Rodney McKay.

Grey canon or gray canon refers to canon that is ambiguous in its canonicity: a detail implied or easily inferred in canon but not confirmed outright; a detail brought up in a creator commentary or podcast but never stated in canon itself. (Essentially, the canonicity of that fact is in a gray area.) An example of grey canon would be the "Previously" segments in Battlestar Galactica, which are not, in fact, previously aired material from an episode. Since the not-actually-Previouslies do not occur within the bounds of an episode, it is not unreasonable to call them non-canonical; but since they affect the episode to which they are attached, it might also make sense to call them part of canon.

Closed vs. Open

A fandom is considered to possess a closed canon when no additional source material is expected to be forthcoming (there are no upcoming books, episodes, or movies in the series). Examples of fandoms with closed canons are Due South, P.G. Wodehouse, and Good Omens.

By contrast, an open canon would thus be one in which new episodes, books, or movies are being produced. Examples of these would be House, Supernatural, and Anita Blake: Vampire Hunter.

Fans of a universe who find it extended in a different medium (as comics following a completed television series, television series following a movie, etc.) sometimes have difficulty agreeing on what constitutes canon. There are Star Trek fans who only believe the first series (ST:TOS) is canon and Homicide: Life on the Streets and Wiseguy fans who deny the "canonicity" of their post-series TV movies. Certainly there are plenty of Star Wars fans who consider Star Wars a closed canon, even though tie-in books are still being published. In some cases, fans look to creators for guidance (e.g., canon for The Sarah Connor Chronicles officially ignores the third movie in the Terminator universe); in others, a rough consensus emerges (e.g., Supernatural comics are generally rejected from canon due to a high continuity-error rate). In still other fandoms, no consensus exists, and creators of fanworks may disclaim extensively exactly what they are and are not willing to consider.

Canon in Real Person Fiction

Canon in Pop Culture

T-Rex of Dinosaur Comics once proclaimed several events in his life to be non-canon, including "any event in which I was embarrassed." ^[1]

References

1. ↑ T-Rex oh man, last night was so non-canon April 06 2004. Accessed October 4, 2008.