Definition of "fanon"

fanon¹

/ˈfænən/

noun
plural fanons
1. A vestment reserved only for the Pope for use during a pontifical Mass.
2. Part of a bishop's mitre. They are the tabs extending down from the mitre, often with a cross near the end of each. See lappet.
3. A maniple.
4. (surgery) A fold of linen laid under a splint.

fanon²

/ˈfænən/

noun
uncountable
1. (fandom slang) Elements introduced by fans which are not in the official canon of a fictional world but are widely believed to be or treated as if canonical.
  Quotations
  In this way, smaller groups within a fandom agree on readings which may be completely at odds with the canon, but which in time acquire legitimacy as fanon.
  2014, Maria Lindgren Leavenworth, Malin Isaksson, Fanged Fan Fiction: Variations on Twilight, True Blood and The Vampire Diaries‎, page 53
  Loyalty is one aspect of Slytherin that canon and fanon readings technically agree on, but fans are significantly more sincere about this characterization.
  2018, Kali DeDominicis, “Fitting Him for Leather Trousers: Fanon and the Reclamation of Draco Malfoy and Slytherin House”, in Amanda Firestone, Leisa A. Clark, editors, Harry Potter and Convergence Culture: Essays on Fandom and the Expanding Potterverse‎, page 97
  So in a fandom as old as Austen's, how does fanon get created?
  2019, Holly Luetkenhaus, Zoe Weinstein, Austentatious: The Evolving World of Jane Austen Fans‎, page 24