Nothing to do with artillery, nor religion despite the term's origins, canon is a term you might see mentioned on occasion and refers to what stories are officially part of a series' continuity. In terms of things Atlantean Publishing has published, you might see references to a Doctor Who Canon, a King In Yellow Canon and, even, a Ken Longman Canon. Canonical stories are those that are 'true' and which should be treated as such by other writers. Non-canonical stories, such as fan fiction, are either optional extras or outright clash with established continuity. There can even be, as the Atlantean version of Doctor Who continuity created, a specific subcanon within such fan fiction. Whether a writer adheres to canon, and how far, is very much a personal matter and we are not 'Canon Nazis' when it comes to things such as the Yellow Mythos (especially as we have published pieces dealing with the very fuzziness of the issue).