an independently controlled tab set in the trailing edge of a control surface, as an elevator, aileron, or rudder, to hold it in a position suitable for stabilizing the aircraft in a flight attitude.
Also, trimming tab.
Examples from the web for trim tab
The elevator trim tab was found attached, and cable continuity was established from the trim tab to the middle of the cabin floor.
The trim tab controller shall be located at the operator's station.
Maintenance personnel investigated and found a bolt and bushing missing from the right elevator trim tab horn.
The horizontal tail plane has a fixed stabilizer with an elevator and trim tab.
The left trim tab is an adjustable tab, which is operated by the pilot.
Where irreversible trim tab control systems are used.
The inboard portion of the trim tab was intact and moved freely.
British Dictionary definitions for trim tab
trim tab
noun
1.
a small control surface attached to the trailing edge of a main control surface to enable the pilot to trim an aircraft