Thank you! The reference to "hash" allowed me to check dictionary.com, and I found this:

Common names: number sign; pound; pound sign;
hash; sharp; crunch; hex; INTERCAL: mesh. Rare:
grid; crosshatch; octothorpe; flash; ITU-T: square,
pig-pen; tictactoe; scratchmark; thud; thump; splat.

I knew there were several unusual words for it.
I had heard the word "octothorpe", and couldn't quite recall it and it has been driving me crazy! Well, maybe now I can get some sleep!

Don