Plain English Meaning
A long screw inside the landing gear mechanism that turns when the motor runs. As it spins, it pushes or pulls the gear up or down — like a screw jack lifting or lowering the wheels.
Full Definition
A threaded rod within an electric landing gear actuator that converts the rotary motion of an electric motor into the linear (push-pull) motion needed to extend or retract the landing gear. As the motor turns the screw, a nut riding on the threads travels along its length, moving the gear linkage with it.
Context Anchor
Seen in discussions of retractable landing gear systems, especially electric gear systems and gear extension or retraction problems.
Derivation
Actuator comes from the Latin actus, meaning 'a doing' or 'a driving' — it's the part that does the moving. Paired with screw, it describes a screw that drives motion, rather than one that simply fastens two things together.