A firearm chambered in 9mm. Properly used, it refers to the 9x19mm cartridge, aslo known as 9mm Parabelum or 9mm Luger. Though several other calibers are 9mm in diameter, they should not correctly be refered to as "nines".
9x17 AKA 9K AKA 9mm Kurtz AKA 9mm short is properly refered to in ghetto slang as a .380, referring to .380ACP the proper American nomenclature.
9x18 AKA 9mm Makarov is not commonly found in North America, and is therefore unavailable to most criminals.
9x21, is a more powerful variation of the 9x19 cartridge, and the two are not compatible in autopistols.
9x23, is a powerful cartridge, but is seldom found in cheap pistols, and therefore out of reach for most criminals.
"bust a nine in he ass"
"how you like that nine in yo spine?"