Definition
Aircraft control systems that relieve the pilot of the need to maintain constant pressure on the flight controls by adjusting small auxiliary surfaces (such as trim tabs) or by repositioning the control surface itself, allowing the aircraft to maintain a desired attitude or flight condition hands-off. Trim is typically available for pitch on most aircraft, and for roll and yaw on more complex aircraft. In autopilot-equipped aircraft, automatic trim systems work in conjunction with the autopilot to keep the aircraft properly trimmed throughout flight.
Plain English
Trim systems take the steady pressure off the controls so the pilot doesn't have to keep pushing or pulling to hold the aircraft where they want it. Once trimmed, the aircraft will fly in that condition on its own.
Context Anchor
Seen in aircraft control, autopilot, and AFCS discussions, and used when setting trim before takeoff, after speed changes, during climbs and descents, and before or after autopilot use.
Derivation
Trim comes from an Old English word meaning 'to set in good order' or 'to balance.' In aviation it carries that same idea -- setting the aircraft in balance so it flies steadily without the pilot fighting the controls.
Why Pilots Care
Proper trim reduces pilot workload, prevents fatigue on long legs, and allows precise hands-free flight especially when coupled with the autopilot.
Intuition Check
Trim does not mean cutting something off or making it look neat here. In aviation, trim means making a small balance adjustment so the aircraft does not need constant control force.
Example Sentence 1
After leveling off at the cruise altitude, the pilot adjusted the pitch trim until the aircraft held altitude with no pressure on the yoke.
Example Sentence 2
Before engaging the autopilot, the crew verified that all trim systems were set for the current airspeed and configuration.