from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. Denoting excitement, surprise, or shock.
- n. Indicates a good move.
- n. Placed after a herbarium abbreviation to indicate that the mentioned material held there has been examined directly by the author.
- n. A Boolean negation, the not operator, serving to invert the truth value of what follows.
- n. Formerly used as a separator between hostnames in an e-mail address for the purpose of routing a message (called bang path notation).
- n. Used as a separator between a user's nickname and ident.
- n. factorial
May derive from a Latin Io, with the I written over the o, placed at the end of an exclamation to mark it as such. The Io may either be an abbreviation for interiectiō ("interjection"), or else the interjection Iō ("hey!"). (Wiktionary)