What are tabs on an airplane?

Trim tabs are small control surfaces which enable the pilot to fine-tune the pitch, roll, or yaw of the aircraft to maintain a specific configuration without the pilot having to constantly exert force on the controls.

A pilot might use the elevator trim tab to put the aircraft in a nose-high climbing configuration without having to keep constant pressure on the yoke.

A pilot would use aileron trim to counteract a natural tendency to roll caused by the aircraft being out of balance.

A pilot would use rudder trim to counteract a natural tendency to yaw left or right due to engine loss, or low airspeed p-factor.