I was going to joke and say "I don't know what it is, but I sure want one"-
Turns out I've got a prehistoric craftsman 113 tablesaw and could actually probably use one.
I need to go look to see if the saw even has the place for this. I think my saw predates the 113 nomenclature. It was certainly made before safety was a concern. I would need the rest of the guard for it to be any good.