Plain English Meaning
What the aircraft can actually do on a given day — how fast it climbs, how far it flies, how much runway it needs, and how high it can go — based on its weight, the weather, and how it's set up.
Full Definition
The measurable capabilities of an aircraft under given conditions, including takeoff and landing distance, climb rate, cruise speed, fuel burn, range, service ceiling, and maneuvering limits. Performance values vary with weight, atmospheric conditions (pressure, temperature, ), (, , ), and aircraft .