A firearm is any type of gun designed to be readily carried and used by an individual. The term is legally defined further in different countries.
Modern firearms can be described by their caliber (i.e. bore diameter). For pistols and rifles this is given in millimeters or inches (e.g. 7.62mm or .308 in.), or in the case of shotguns by their gauge (e.g. 12 ga. and 20 ga.). They are also described by the type of action employed (e.g. muzzleloader, breechloader, lever, bolt, pump, revolver, semi-automatic, fully automatic, etc.), together with the usual means of deportment (i.e. hand-held or mechanical mounting).