Global Positioning System
(GPS) A system for determining postion on the Earth's surface by comparing radio signals from several satellites. When completed the system will consist of 24 satellites equipped with radio transmitters and atomic clocks.
Depending on your geographic location, the GPS receiver samples data from up to six satellites, it then calculates the time taken for each satellite signal to reach the GPS receiver, and from the difference in time of reception, determines your location.
["Global Positioning by Satellite"? Precison? Coverage? Web page?]