Yeah, it’s an interesting one. I’ve always known it as the hash symbol from back in the 80s when I got my first microcomputer. This was in the UK but I don’t think hash is UK-specific terminology: “shebang” (“hash bang” for #!) has been common parlance amongst the UNIX-crowd since I don’t know when.

I know pound is incredibly common in the US, but in the UK it’s never referred to that way because here pound means £.

“Octothorpe” is entirely new to me though, and I guess is quite context specific?