Forked Fanon is fan-created material that conflicts with existing Erfworld Canon. This material may unwittingly have been created with a conflict, or may have been rendered invalid by a newly introduced piece of canon. Either way, such fan material is now Forked Up.
Forked up material that can be reintegrated to make sense again becomes Fanon again, and all is well. Forked up material that may never be integrated (for example, a short story about Bogroll's life after the Battle for Gobwin Knob) becomes Banon.