And if it isn't obvious, "shebang" is most likely a slang variation of "hashbang" where "hash" is a term sometimes used for "#" and "bang" is a short form for "exclamation mark".
#!
Some people say the "sh" in "shebang" comes from "sharp" which is a musical term for "#" and some say it comes from the shortcut for the standard shell "/bin/sh" but I don't believe either of those theories.