Definition
An adjustment of the elevator trim system that holds the elevator in a position which causes the airplane's nose to pitch up, relieving the pilot of the steady back pressure that would otherwise be required on the control column to maintain a higher pitch attitude.
Plain English
Setting the trim so the airplane wants to hold its nose higher on its own, so the pilot does not have to keep pulling back on the controls.
Context Anchor
Used when establishing or maintaining a climb, after the pilot has set power and adjusted pitch attitude.
Derivation
"Trim" comes from the old nautical sense of adjusting a vessel so it sits balanced in the water. In an airplane, trimming balances the control forces so the pilot does not have to fight the controls to hold an attitude.
Why Pilots Care
It reduces control pressure and pilot fatigue, allowing more precise and relaxed pitch control throughout the climb.
Intuition Check
Nose-up does not automatically mean the airplane is climbing; it means the nose is being held at a higher attitude. Whether the airplane actually climbs also depends on power and airspeed.
Example Sentence 1
After establishing the climb attitude and full power, the pilot added nose-up elevator trim until the back pressure on the yoke was relieved.
Example Sentence 2
With a few turns of nose-up elevator trim applied, the airplane held a steady 500-foot-per-minute climb with almost no further control input.