Fanon

Fanon, simply put, is a so-called "fact" that someone thinks is true but has no evidence of in any official material, and by some means of outstandingly complex and confusing contrivance, gets picked up by other fans. This includes terms like Herald of Unicron. While none of there terms exist within any of the official canon of the Transformers multiverse, they are wide-spread and accepted, and will at times even become canon if the writers use retcon or accept the fans' opinion of a certain story.

From Teletraan I: The Transformers Wiki, a Wikia wiki.