What is Fanon?
Fanon takes fiction a step further. A derivation from the words 'fan' and 'canon', a fanon is a situation, created by a fan, instead of a pure canon. These are commonly accepted ideas among fan fiction writers and creators but don't necessarily feature in the canon work. If a concept is used only once in the entire series of the canon work, the fan fiction creators may capitalize on it and use it more than once in their work. This also constitutes fanon work.
Mostly fanon created by fans becomes so popular that many fans believe it to be true, even if it has not occurred in the original piece. Fanon is not generally contradictory to the original work, but takes certain liberties when explaining certain actions or situations. Such fanon can mostly be seen in relation with television series, books and movies. Fans mostly present their take on a particular scene in a book or movie, which though not changing the storyline entirely, does give a fresh and unique approach to the scene.
The fact that fanon does not entirely contradict canon, makes it more popularly accepted by fans, sometimes even more than the original. Some of the more widely known fanon includes, Emperor Palpatine's first name, in Star Wars, is Cos, SiriusxLupin, from Harry Potter and many others. Many fans also use fanon to showcase their own skills, hoping that the piece catches on and gets noticed by the right people. Opening many doors for the writer as well as the story, as fanon is a great way to let your imagination run wild.
Also fanon is a great way to express discontent regarding a turn of events, or plotline and many fans are known to provide creative fanon, which though not changing the flow of events, gives a different approach to a scene. So if there is a particular ending you wanted for your favorite book, go ahead and write it out, and be sure to share it with the world. Just remember that your piece needs to stay true to the spirit of the original masterpiece, and though different routes are allowed in fanon the destination needs to be the same.