Plain English Meaning

The whole horizontal tail can pivot up or down to keep the aircraft balanced in pitch, instead of using just a small tab on the elevator.

Full Definition

A horizontal tail surface whose angle relative to the aircraft's longitudinal axis can be adjusted in flight, allowing the entire stabilizer to be repositioned for pitch trim rather than relying solely on a small trim tab on the elevator. It is used on many transport-category and high-speed aircraft to provide effective trim across a wide range of speeds and center-of-gravity .