Battlestar Wiki:Canon
From Battlestar Wiki, the free, open content Battlestar Galactica encyclopedia and episode guide
Canon describes those people and events that are an official part of a fictional universe.
The term is used to distinguish those "facts" about and within a fictional universe that are accepted against those that are hypothesised by fans and/or the result of novels and other spin-offs that may not be recognised by the original creators. For example, there have been a great many novels written about Star Trek portraying various adventures of the characters. These novels are non-canonical, and their events did not "actually occur" within the Star Trek universe.