Plain English Meaning
Stopping a climb or descent and settling the airplane into steady flight at the altitude you wanted to reach.
Full Definition
The transition maneuver from a climb or descent to level flight at a target altitude, accomplished by smoothly adjusting pitch attitude and power so the aircraft arrives at the desired altitude with zero vertical speed and the selected airspeed.
Context Anchor
Seen during instrument flying when using the attitude display, altimeter, vertical speed indication, and to judge when the airplane is about to stop climbing or descending.