Definition 1 of 2
Definition
Small adjustable surfaces or mechanisms on an aircraft's flight controls that relieve the pilot of the need to hold continuous pressure on the controls to maintain a desired flight attitude. Trim devices include trim tabs on the trailing edges of elevators, ailerons, or rudders, as well as adjustable stabilizers and spring or bungee systems, all of which allow the aircraft to fly hands-off in a chosen pitch, roll, or yaw configuration.
Plain English
Parts of the controls that let the pilot 'set' the aircraft so it stays in the desired attitude on its own, without the pilot having to keep pushing or pulling on the yoke or pedals.
Context Anchor
You encounter trim devices during preflight checks, before takeoff, in cruise flight, during climbs and descents, and whenever a checklist tells you to set or check trim.
Derivation
Trim' comes from the Old English trymman, meaning to make firm or set in order. The same word is used in sailing to describe adjusting sails so the boat holds its course steadily — a useful image for what trim devices do for an aircraft.
Why Pilots Care
Reduces control pressure, lowers pilot fatigue, and helps maintain stable flight with minimal workload.
Analogy
Like cruise control on a car — once set, the aircraft maintains the chosen condition without constant input from the pilot.
Intuition Check
Trim here does not mean decoration or cutting something off. It means adjusting the airplane so it does not require constant hand pressure to hold the desired flight path.
Example Sentence 1
After establishing the climb, the pilot used the trim devices to relieve the back pressure on the yoke.
Example Sentence 2
During the before-takeoff checklist the pilot verified the trim devices were set for the computed takeoff weight.