The word fanon is a mixture of the words 'fan' and 'canon', and is when events related to television, books, games and films have been written so many times by fanfiction writers that it almost becomes canon. In other words, it ends up being believed that the events have happened in the actual books, films and so on when in fact it hasn't.
Fanon can also apply to characters from film and books and so on. A character may be portrayed a certain way so many times that it seems as though they have the same personality in the books, or fans begin to believe that the character will become that way.
Sometimes, fanon can actually be considered to be better than the original works. This could be because fans didn't agree with a particular storyline in the original work, and they feel that their fanon view would work better.
Fanon can also apply to characters from film and books and so on. A character may be portrayed a certain way so many times that it seems as though they have the same personality in the books, or fans begin to believe that the character will become that way.
Sometimes, fanon can actually be considered to be better than the original works. This could be because fans didn't agree with a particular storyline in the original work, and they feel that their fanon view would work better.