Canon is another word for official. The primary use of the term is to distinguish official settings and stories from individual troupes' chronicles and other fan-made fiction and resources. The secondary use of the term is to establish the official facts of a fictional setting (and, sometimes, to retroactively alter those facts in a retcon). Generally speaking, when the term "canon" is used on this wiki, the use of both definitions is implied.
The White Wolf canon is generally defined as all official game books released by White Wolf Publishing. The various "official" references (such as the novels) may be used as a guide to canon information, but are not necessarily canon in and of themselves. The Kindred: The Embraced TV series and the various White Wolf collectible card games and video games are not strictly considered canon (although the relevant material is still considered appropriate for posting on this Wiki). Fan works are, by definition, not canonical, although ideas and terms from the fan community are often accepted as an unoffical part of the canon by the fan community; these ideas are dubbed "fanon" (from "fan canon").
Game books produced under license from Onyx Path Publishing are currently considered to be canonical, and the new licensed LARP material from By Night Studios is based off of the Classic World of Darkness setting but diverges into its own canon, although either or both of these relationships with canon may change in the future as White Wolf (under the management of Paradox Interactive) resumes the development of World of Darkness material in-house.
The definition of White Wolf canon may vary for different fans, and therefore for a reference source like the WWWiki, the question may become especially difficult.