Plain English Meaning
A map of the airport itself, showing all the runways, taxiways, and buildings, so a pilot knows where everything is and how to get around on the ground.
Full Definition
A scaled drawing of an airport showing the layout of runways, taxiways, ramps, terminal buildings, and other ground features, used by pilots to navigate on the ground and orient themselves at the airport.
Context Anchor
Pilots use an airport diagram during preflight planning, taxi planning, and ground operations at both familiar and unfamiliar airports.
Derivation
Diagram comes from Greek words meaning “marked out by lines.” That fits this use because an airport diagram is not a photo; it is a line drawing that marks out the airport layout clearly enough to use while operating on the ground.