Canon refers to the official, authentic version of something, especially in stories, religious texts, or works of art. When fans debate whether something is canon in a story, they're asking if it's part of the real, accepted version that the original creator intended.

In literature and entertainment, canon matters a lot. The seven Harry Potter books are canon, but fan fiction about the characters isn't. The original Star Wars movies are canon, but many of the expanded universe books were later declared non-canon. When a movie sequel contradicts something from an earlier film, fans might argue about which version is truly canon.

The word originally comes from religious contexts, where the biblical canon refers to the books officially accepted as Scripture. Religious scholars spent centuries determining which ancient texts belonged in the canon and which didn't.

In music, a canon is also a completely different thing: a piece where one melody is played and then repeated by other voices or instruments, starting at different times, like “Row, Row, Row Your Boat” when sung as a round. This musical meaning shares the idea of a pattern that others follow.