GPS
From DictionGloss
Global Positioning System, navigation satellites transmit specially coded signals, processed by a receiver that computes extremely accurate measurements, including 3-dimensional position, velocity, and time on a continuous basis. A DoD conceived, implemented and operated constellation of 24 satellites orbiting the earth at a nominal altitude of 11,000 miles. GPS satellites transmit signals that allow the accurate determination of GPS receiver locations. Receivers can be located at fixed locations, moving on the earth's surface, in the earth's atmosphere, or in low-Earth orbit.
GPS is used in air, land and sea navigation, mapping, surveying and other applications where precise positioning is necessary. The GPS signal is provided free of charge to anyone on or near the planet with a GPS receiver and an unobstructed view of the satellites.