Plainclothes law enforcement in the context of "Sidearm (weapon)"

A sidearm is an individual-served weapon that is kept at one's side and can be rapidly accessed if needed. A sidearm may be carried alone or as an ancillary weapon to a more frequently-used primary weapon. The term historically referred to swords, daggers, and similar small weapons kept at one's side in a sheath, and in modern combat dominated by guns, sidearms are often defined as handguns that are similarly kept in a holster.

A sidearm is typically required equipment for military officers and may be carried by law enforcement personnel. Usually, uniformed personnel of these services wear their weapons openly, while plainclothes personnel have their sidearms concealed under their clothes.