The handful of questions in the tag interpret it rather loosely. Should we clarify/synonymize or delete this tag (and related tags like concept, which don't yet exist but could easily be pre-emptively captured in this discussion)?
I don't see that this tag adds any value as-is; I am personally in favor of adding it to the blacklist.
I can't see a useful path towards clarifying it. The obvious attempt, "game-concepts," seems like just another way to say game-design except that it invites opinion-based questions like "here's my game concept, what do you think?" which aren't on-topic here.
The tag is often used in a way that seems to simply categorize the question, as in "I don't actually have this problem, I'm just thinking about the problem conceptually." It's not useful in that context.
Consequently, I think it should be removed.