We've been seeing a lot of trivia reports lately regarding whether a question is "canon" or not. For example, the card game. So let's make clear the definition.

Canon: Another word for official. Used quite often in fan fiction to differentiate between the official storyline in which the fan fiction is based on.

That's essentially it in a nutshell. Canon doesn't mean "just the series". It has to do with any and all official and factual knowledge regarding the Avatar universe. AKA, "from the minds of the OFFICIAL creators of the show".
Examples: Canon=Yangchen, Kuruk, Umi, etc. Not canon="Gaang", "Kataang", "Zutara", and all that other "shipping" nonsense.

So please, no more reports on "the card game isn't canon because it's not the show!"...PLEASE. Just because some of us don't play the card game doesn't make it any less canon/official.