Conversation so far:
what does it mean when something is canon?
In fiction, canon is the material accepted as officially part of the story in the fictional universe of that story.
does the work have to be from the original author to be canon?
In literature the term canon is used to distinguish between the original works of a writer who created certain characters and/or settings, and the later works of other writers.

Question: what is an example?
Self-contained rewrite: what is an example of canon in literature to distinguish between the original works and later works of other writers?