From SKYbrary Wiki
A target reverser is a hydraulically actuated system that uses bucket type doors to reverse the flow of the engine hot gas stream. Whilst in forward thrust, the bucket doors form the final tail pipe nozzle of the engine. When reverse thrust is selected by the pilot, actuators close the buckets over the hot gas stream deflecting it forward. A mechanical lock holds the buckets in their extended position to allow thrust to be increased without the associated risk of an uncommanded, asymmetric retraction of the buckets.