Definition
A condition of flight in which the aircraft maintains a steady attitude and flight path without the pilot needing to hold pressure on the controls, achieved by adjusting the trim devices so the aerodynamic forces on the control surfaces are balanced.
Plain English
The aircraft is flying steadily on its own, hands-off, because the trim has been set so the controls don't need to be held in position.
Context Anchor
Seen in aircraft handling, flight control rigging, trim tab adjustment, and pilot reports about control forces.
Derivation
The word 'trim' comes from the Old English 'trymman,' meaning to set in order or arrange. In sailing it referred to adjusting sails for balance. In aviation it carries the same idea: arranging the control surfaces so the aircraft is balanced and steady.
Why Pilots Care
Allows stable flight with reduced pilot workload and prevents control-surface fatigue on longer flights.
Analogy
Like setting the cruise control on a car so the vehicle holds speed without constant pressure on the accelerator.
Intuition Check
Trimmed does not mean the airplane has been cut or made smaller. Here, trimmed means adjusted into balance so the controls do not need constant pressure.
Example Sentence 1
Once established in cruise, the pilot adjusted the elevator trim until the aircraft was in trimmed flight at 4,500 feet.
Example Sentence 2
During cruise, the pilot confirmed trimmed flight by releasing the controls and observing no pitch change.