What is "fanon"?

Fanon is a conclusion made from various facts presented and lead the audience/readers to believe that something is true, but not necessarily part of the canon. For example:

Helia is a wizard because his uncle, Saladin, is a wizard.

In the Winx Club, it's assumed that people inherit magic. If Saladin is a wizard, we would assume that the parent of Helia related to Saladin is a witch or a wizard as well. Therefore, Helia should also be a wizard.

However, Helia nor Saladin have ever stated that Helia is a wizard. Helia has never clearly demonstrated the ability to cast magic. Because of this, the above statement is neither true or false.