Comic Book Terms – Canon
What is a Canon? Similar to internal continuity, the “canon” of comics characters/universes is often subject to change, but refers to the stories which are, at any one point, part of the “official”, “accepted” history and story of particular characters/universes. Alternate versions of characters (such as DC’s Elseworlds and Marvel’s speculative What if…? titles) are necessarily not canon. However, stories can change from being non-canonical to being accepted as canon – and vice versa. In particular, line-wide continuity-changing events (such as DC’s Crises, New DC 52 and Marvel’s controversial Spider-Man: One More Day storyline) retroactively affect which stories are part of a character/universe’s core canon, as they may revise or ignore previous events and happenings.
For example, DC’s Crisis on Infinite Earths addressed continuity and consistency errors over almost 50 years of comics publication, and retrofitted events and characters into the history of the DCU as if they had always been there. (For example, the JSA went from being JLA-contemporaries from a parallel world to being their earlier, historical counterparts some years previously.) The Post-Crisis DC Universe removed many stories from “official canon”, explaining them as Imaginary Tales or ignoring them completely. The New DC 52 has also recently reset DC canon.