In general, the word "canon" refers to a set of works that are considered part of the genuine story by the author.

That means, here, that the canon (or that which is canonical) are words and rules that are shown in-game (in TES V: Skyrim). The non-canon is what we came up with. Like fan-fiction. The non-canon is subject to change (a lot), but the canon is pretty much set in stone (word-wall joke).

This is mentioned in the non-canon Memrise course and in the learning pages.

Semi-canon is a word based off of canon, but isn't. 

Affixes don't affect the canon level.

Non canon is fan words, and canon is straight from the game, and so far only one word from the game we don't know and its "laar"