Plain English Meaning
How GPS works: the receiver listens to several satellites, works out how far away each one is, and uses that to figure out exactly where the aircraft is and where it's going.
Full Definition
The way the Global Positioning System determines an aircraft's position by receiving timed signals from a network of orbiting satellites and calculating the distance to each one. The receiver compares signals from at least four satellites to compute a three-dimensional position (latitude, longitude, altitude) and precise time, which it then uses to provide navigation guidance such as track, groundspeed, distance, and bearing to a chosen waypoint.