What is IRC Hostmask ?

Answer 1

A full IRC hostmask contains the nick, ident and an IP, they are separated by an exclamation mark (!) and an at (@).
The exclamation mark separates the nick from the ident (nick!ident), the at separates the ident from the IP (nick!ident@IPaddress).
The separators are always used in a ban and they always stay on the same place, the nick/ident separator ! on the left, the ident/IP separator @ on the right.

A full hostmask looks like this: nick!ident@IPaddress