Plain English Meaning
A height above the ground that gives you enough room to practice flight maneuvers safely, with space to recover if something goes wrong before you get near the ground.
Full Definition
An altitude high enough above the ground to allow a pilot to safely perform training maneuvers, typically providing adequate margin for recovery from stalls, steep turns, or unusual attitudes without risk of ground contact. For most general aviation training maneuvers, this is no lower than 1,500 feet AGL, though specific maneuvers (such as those involving stall recovery) require greater altitudes.