Definition
A horizontal stabilizer whose angle of incidence (the angle at which it meets the oncoming airflow) can be changed in flight by the pilot or the trim system, allowing the airplane to be trimmed for hands-off level flight across a wide range of airspeeds, weights, and center-of-gravity conditions.
Plain English
It is the small horizontal wing at the tail of the airplane, but built so the whole surface can tilt up or down. By tilting it, the pilot adjusts the airplane's natural balance so it flies steady without having to hold pressure on the controls.
Context Anchor
Seen in discussions of pitch trim, airplane tail design, preflight checks, and takeoff trim settings.
Derivation
Stabilizer comes from the Latin stabilis, meaning steady or firm. The horizontal stabilizer is the tail surface that keeps the airplane steady in pitch. Adjustable simply means its position can be changed, rather than being fixed in place.
Why Pilots Care
Correct adjustment removes control forces so the airplane maintains altitude and airspeed with little effort, lowering workload and fatigue.
Intuition Check
Do not confuse an adjustable stabilizer with an elevator. The elevator moves as a primary flight control; an adjustable stabilizer changes the angle of the tail surface itself, mainly to help balance the airplane.
Example Sentence 1
Before takeoff, the crew set the adjustable stabilizer to the position called for by the loading data.
Example Sentence 2
During the preflight inspection the adjustable stabilizer was moved through its full range to confirm free movement.