A turret was a type of weapon. In space, turrets were small unmanned defensive platforms which were used for protective purposes in the absence of starships. They had no propulsion system, and so were transported using starship tractor beams.
By 2333, Starbase 61 was complemented with six defensive platforms in the Phidian system. That year, the crew modified the turrets to increase their range in power. Deployed by Starfleet vessels via tractor beam over the inhabited planets in the system, these turrets provided a defense against incoming stellar debris.