A handgun is a firearm designed to have the potential to be held and operated by one hand, although not necessarily used that way. This characteristic differentiates handguns as a general class of firearms from long guns such as rifles and shotguns (which are mounted against the shoulder).

Major handgun subtypes are the revolver and pistol; other subtypes include derringers, single-shot pistols, semi-automatic pistols, pepperboxes, and machine pistols.

The overlapping variations in meaning of the words "pistol" and "handgun" are discussed below.

Although handgun use often includes bracing with a second hand, the essential distinguishing characteristic of a handgun is its facility for one-handed operation.

The word "pistol" is often synonymous with the word "handgun". Some handgun experts make a technical distinction that views pistols as a subset of handguns. Sometimes in American usage, the term "pistol" refers to a handgun having one chamber integral with the barrel, making pistols distinct from the other main type of handgun, the revolver, which has a revolving cylinder containing multiple chambers. But UK/Commonwealth usage often does not make this distinction. For example, the official designation of the Webley Mk VI was "Pistol, Revolver, Webley No. 1 Mk VI", and the designation "Pistol No. 2 Mk I" was used to refer to both the Enfield Revolver and the later Browning Hi-Power semi-automatic.