Definition
A small, hinged auxiliary surface attached to the trailing edge of a primary flight control surface (such as an aileron, elevator, or rudder). The tab deflects into the airflow to produce an aerodynamic force that helps move or hold the larger control surface in the desired position, reducing the control pressure the pilot must hold.
Plain English
A small flap on the back edge of a control surface that uses the airflow to take the load off the pilot, so they don't have to keep pushing or pulling the controls.
Context Anchor
Seen during preflight inspections, flight control discussions, trim system checks, and maintenance descriptions of elevators, rudders, and ailerons.
Derivation
The word "tab" has long been used for a small projecting piece or flap attached to a larger item. That helps here because an aircraft tab is exactly that: a small attached surface that affects the larger control surface.
Why Pilots Care
Tabs reduce pilot workload and allow hands-off flight at a desired attitude, directly affecting control feel and fatigue on longer flights.
Intuition Check
Do not think of a tab as a label or a page marker here. In aircraft use, a tab is a small movable control surface attached to a larger one.
Example Sentence 1
After leveling off in cruise, the pilot adjusted the elevator trim tab until the airplane held altitude with no pressure on the yoke.
Example Sentence 2
During the preflight walk-around, I verified that the rudder tab moved smoothly with the control input.