Is not every question about some concept? I'm wondering if this is not way too unspecific to be a useful tag at all.
It's a bit like having a 'numbers' tag on Math.SE. I could see the use of 'number-theory' ('concept-theory'?) or specific cases like 'prime-numbers' (are there equivalents for 'concept'?), but 'numbers' or 'concept' just seems a bit too broad.
What do you think? Should the tag be removed?