When applied to Freespace, Canon is anything that has been confirmed as official truth within the Freespace universe by Volition. This is largely limited to in-game data, most often from either mission briefings and debriefings, Command briefings, in-mission messages, cut-scenes and the tech room, however a few other, non in-game sources can be considered canon, such as the Freespace Reference Bible. All other information is non-canon and should not be treated as official.
Non-canon information is not entirely disallowed on the Freespace Wiki. However, when submitting anything, canon information should take precedence; non-canon information should always be clearly labelled as such and, wherever possible, separated from the main article through use of the non-canon tag:
It can be used in an article with the following tag: {{non-canon}}
If this is not possible, ensure that non-canon data is clearly marked through other means, for example, asterisks (*) with a footnote at the base of the page.