Rotating gun turrets have the protection, the weapon, and its crew rotate. When this meaning of the word "turret" started being used at the beginning of the 1860s, turrets were normally cylindrical. Barbettes were an alternative to turrets; with a barbette the protection was fixed, and the weapon and crew were on a rotating platform inside the barbette. In the 1890s, armoured hoods (also known as "gun houses") were added to barbettes; these rotated with the platform (hence the term "hooded barbette"). By the early 20th Century, these hoods were known as turrets. Modern warships have gun-mountings described as turrets, though the "protection" on them is limited to protection from the weather.
Rotating turrets can be mounted on a fortified building or structure such as a coastal blockhouse, be part of a land battery, be mounted on a combat vehicle, a naval ship, or a military aircraft, they may be armed with one or more machine guns, automatic cannons, large-calibre guns, or missile launchers. They may be manned or remotely controlled and are most often protected to some degree, if not actually armoured.
The protection provided by the turret may be against battle damage, the weather conditions, general environment in which the weapon or its crew will be operating. The name derives from the pre-existing noun turret meaning a self-contained protective position which is situated on top of a fortification or defensive wall as opposed to rising directly from the ground, in which case it constitutes a tower.
A small turret, or sub-turret set on top of a larger one, is called a cupola. The term cupola is also used for a rotating turret that carries a sighting device rather than weaponry, such as that used by a tank commander.