Fanon

The term Fanon is a portmanteau of "fan" and "canon". The term is used to refer to non-canon commonly confused as canon or to fan-made Star Wars fiction. Fan fiction (also spelled fanfiction and often abbreviated to fanfic) is a fiction written by fans that takes place in the Star Wars universe. Such fiction is never regarded as canon.

Fanon assumed as canon
Some fanon is considered "community wide". It applies to certain "facts" that may have been accepted as a truth by a large number of fans, although not necessarily true, and thus either replaces an established canonical fact in the minds of those fans, or fills a plot-hole.

One example of this form of canon is the mystery of Palpatine's first name; many fans have adopted "Cos" as the Emperor's first name, from early drafts of George Lucas's work.

Fanon made official canon
Fanon is occasionally adopted by Expanded Universe authors, such as the existence of the 501st Legion, and so becomes canonical. The What's the Story? competition invites members of the Hyperspace fanclub to submit fan written backstories to selected characters, the best of which will be accepted as the official backstories and entered into the database. This is one of the very few examples where fanon is systematically introduced into the canonical continuity. The selected submissions, however, are typically of a high quality and credibility.

Fanon which is accepted officially as part of the Star Wars canon ceases to be fanon.

Individual fanon
Fanon can also take the form of personal beliefs held by individuals. In this case, an individual may create an expansive backstory, possibly a fan fiction, which he or she accepts as "true."

Fanon on Wookieepedia
Wookieepedia generally does not accept any form of fanon whatsoever, because the purpose of Wookieepedia is to document officially canonical elements of the Star Wars universe. Occasionally articles of very widespread fanon in the community are created, but these are tagged as being non-canonical and are not presented as if they were part of the official canon.

Addition of fanon material to existing articles as well as the creation of new fanon-based articles is considered vandalism and may be grounds for permanent bans. Only on user pages is fanon allowed, provided that it is clearly marked as fanon and is limited to a very small amount. Many user pages contain individual fanon based on Mary Sue-ish fan fictions.