A pistol is a handgun whose chamber is integral with the barrel, as opposed to revolvers with multiple chambers being incorporated into a cylinder. The most prolific pistol designs include the derringer, single-shot pistol and the autoloader.
Modern self-loading pistols mostly use rimless centerfire cartridges, although there's a long history of pistols chambered in rimfire (.22 LR Beretta 70), semi-rimmed (.32 ACP Walther PPK), or even revolver (rimmed centerfire) calibers (.357/.44 Magnum IMI Desert Eagle). Most semi-automatic actions show several feeding reliability issues with rimmed cartridges, though.
This tag implicates gun.