Canon is a real-life term for events that have happened in the Star Wars universe. There are various types of Star Wars canon.
G-canon is "George Lucas" canon; the six Episodes and anything directly provided to Lucas Licensing by Lucas (including unpublished production notes from him or his production department that are never seen by the public). Elements originating with Lucas in the movie novelizations, reference books, and other sources are also G-canon, though anything created by the authors of those sources is C-canon. When the matter of changes between movie versions arises, the most recently released editions are deemed superior to older ones, as they correct mistakes, improve consistency between the two trilogies, and express Lucas's current vision of the Star Wars universe most closely.
C-canon is "continuity" canon, consisting of all recent works (and many older works) released under the name of Star Wars: books, comics, games, cartoons, non-theatrical films, and more. Games are a special case, as generally only the stories are C-canon, while things like stats and gameplay may not be; they also offer non-canonical options to the player, such as choosing female gender for a canonically male character. C-canon elements have been known to appear in the movies, thus making them G-canon; examples include the name "Coruscant," swoop bikes, Quinlan Vos, Aayla Secura, YT-2400 freighters, Salporin, and Action VI Transports.
S-canon is "secondary" canon; the materials are available to be used or ignored as needed by current authors. This includes mostly older works, such as much of the Marvel Star Wars comics, that predate a consistent effort to maintain continuity; it also contains certain elements of a few otherwise N-canon stories, and other things that "may not fit just right." Many formerly S-canon elements have been elevated to C-canon through their inclusion in more recent works by continuity-minded authors, while many other older works (such as The Han Solo Adventures) were accounted for in continuity from the start despite their age, and thus were always C-canon.
N-canon is "non-canon." What-if stories (such as stories published under the Infinities label) and anything else directly and irreconcilably contradicted by higher canon ends up here. N-canon is the only level that is not considered canon by Lucasfilm.
Fanon or fan canon is a term for non-canon material created by fans. One of the most notable fanon creators, is Mickey Suttle under the name of "SuperShadow". He created such things like giving Palpatine the name "Dantius Palpatine". However, the name "Dantius" has been deemed non-canon, or in this case, fanon since it was created by a fan.
Fanon on SWGamesEdit
Currently, SWGames does not accept fanon, nor will it ever. Such things will be kept on user pages and only there. If a user wishes to contribute to a Star Wars encyclopedia to create fanon, the best place to go is to the Star Wars Fanon Wiki where such things are allowed.