Plain English Meaning
A built-in digital library inside the aircraft's navigation equipment. It holds the location and details of airports, navigation aids, routes, and instrument procedures so the system knows where things are when the pilot selects them.
Full Definition
Electronic data files stored in onboard navigation equipment (such as GPS receivers and flight management systems) that contain coded information about waypoints, airways, navaids, airports, runways, instrument procedures, and related navigation reference data used by the aircraft to compute position, routing, and procedure guidance.