'hash' is an alternate ... which meaning of hash - drugs, twitter hashtag symbol, computer hashing function, or food?
It's probably drugs, I've heard "costo" in that context, but never in the others. "Hashtag" is a word we use nowadays and the hashing function gets translated as "funciones hash", apparently. I didn't even know about the food but the Spanish Wiki calls it "hash" too.
Just a note, this: # even if now gets called by the English name in certain contexts, it's actually called "almohadilla" in Spanish ;]