I just saw the tag "building-physics" on a question about tire-balancing beads. Which seemed strange to me, as car tires have nothing to do with buildings.
On checking the tag wiki... there's nothing. Which isn't helpful. To me, "building-physics" sounds synonymous with "structural-engineering".
On checking the questions with the tag it doesn't appear that it's being used as a synonym for "structural-engineering", but then I can't see any common theme running through those questions at all!
My primary suggestion is therefore to burninate the tag. Should someone be able to tell me what the tag actually means, and write that into the tag-wiki, then I think the tag would justify retention.