There is so much fan fiction out there that even not counting the movies, it is as if the Harry Potter universe has been extended. Some people use the term “fannon” to describe ideas that are so common that people think they come from cannon, even though they originate from the fans.
This section is my reaction to things that are about the universe, but not part of what I consider cannon.
Note
Binns could be seen as an example of this, but I cover that on his personal page.