This policy describes the canonicity of sources to TV shows, books, and other media.
What is canon? edit
Canon is a formally recognized work that constitutes the official events of the show, movie, or book.
What sources are canon? edit
TV shows edit
For TV shows, the only canon source are aired episodes. Spoilers, despite the fact that they will be in an episode, are not canon. If a TV show has "supplementary material", such as Heroes, which has graphic novels, the events of the material is considered "near-canon"; that is, any information that doesn't contradict aired episodes can be considered true.
Books edit
For books, only the events of the book or books (if it is a series) is canon. "Spin-off books", that is, books that take place within the series' world (such as Fantastic Beasts and Where to Find Them, a spin-off of Harry Potter) are not canon.