Plain English Meaning

Resetting the trim so the aircraft holds its new attitude on its own, without you having to keep pushing or pulling on the controls.

Full Definition

The act of readjusting an aircraft's trim setting after a change in airspeed, power, configuration, or load so that the aircraft once again maintains the desired attitude with minimal or no control pressure from the pilot.

Context Anchor

Seen in flight control and trim tab discussions, and used in flight after changes such as leveling off, changing power, or changing speed.

Derivation

The prefix 're-' means 'again.' So retrimming simply means again — adjusting the trim a second (or third, or fourth) time as change.