Questions about whether a particular work is considered to be official within a fictional universe. DO NOT USE this tag to signify you want answers to your question to be based on (some level of) canon for the franchise. Always use in conjunction with the relevant work tag.
This tag is appropriate for questions about whether a given work (a movie, book, episode, etc.) is considered official within the fictional universe where it takes place. This is a common question in universes that have stories in a wide range of media.
Wikipedia has a more detailed definition of canon.