Basically, anything that isn't relevant to the question, including joke nonsense things like "to hide or not to hide, that is the question." The point of the tags is to make it easier for people searching for those things when the key words pop up. Also, here are a few others:
"Question"-You don't have to put this in since it's understood to be a question.
"Pokemon"-It's Pokemondb, so if it wasn't about pokemon, it would've been hidden, right? This doesn't really narrow things down.
the idea is to extract the key points of what you're asking, and put them into small words, i.e. tags.