Plain English Meaning

A small flap on the back edge of a flight control that does the heavy lifting for the pilot. When you move the controls, the little flap moves first, and the airflow pushing on it swings the bigger control surface into place — so you don't have to muscle it yourself.

Full Definition

A small auxiliary control surface hinged to the trailing edge of a primary flight control (such as an elevator, rudder, or aileron) that moves in the opposite direction to the primary surface. When the pilot moves the cockpit control, the servo tab deflects first, and the aerodynamic force on the tab then drives the larger primary surface into . This reduces the physical effort required from the pilot to move the control.