Terminology - This tag should be used in questions regarding terms and their use.
Consider these two questions:
When I asked what canon means, I actually had no idea of its definition. I see that everyone loves using this term based around anime and manga, and I get the vibe that people use it to describe something as legitimate, but I truly didn't know what it meant (not a troll question).
With that said, my canon question is closed for being off topic, but the tsukkomi question was kept open. In general, both words seem to be associated and used with anime, however, the titled question itself does not pertain to Anime whatsoever.
The only real difference I see between questions is that the tsukkomi question cites a manga description, thus enabling it to be on topic. Otherwise it would be offtopic if it didn't include any anime references and the answer doesn't require any anime references.
In terms of relevancy and usage, I do believe canon is a more common word associated with anime than tsukkomi. Based on that, I would like to think that it can be an on topic question. Perhaps rephrasing the question as What does it mean when an anime is referred to as canon? would make it on topic.
What qualifies as on topic terminology questions?