Plain English Meaning
The set height above the ground that pilots fly when circling the airport to land or after taking off. For most small airplanes this is 1,000 feet above the runway.
Full Definition
The specified altitude, measured above ground level, at which aircraft fly the rectangular circuit around an airport when arriving or departing. It is typically 1,000 feet AGL for propeller-driven airplanes, though it may differ at specific airports as published in the Chart Supplement.
Context Anchor
You encounter this term when planning an arrival, departing an airport, or flying the airport traffic pattern.
Derivation
Altitude comes from the Latin word altus, meaning . That helps here because the term is about the height used in the airport , not the ground path or shape of the pattern.