Plain English Meaning
A system that flies and lands the airplane by itself in an emergency, without the pilot doing anything, after a passenger or pilot presses a single button.
Full Definition
An automated flight system feature that, when activated, takes full control of the airplane and lands it at a suitable airport without any pilot input. The system selects an airport based on weather, runway length, fuel remaining, and terrain, communicates the situation via radio, navigates to the chosen airport, configures the airplane for landing, lands, and brings it to a stop on the runway.