Global positioning system has 3 different meanings across 2 categories:
a navigational system involving satellites and computers that can determine the latitude and longitude of a receiver on Earth by computing the time difference for signals from different satellites to reach the receiver
Any system which enables a mobile receiver to determine its precise location based on signals received from satellites such as those of the US military, the Russian GLONASS system, or the proposed Galileo European alternative system.
A system which enables a mobile receiver to determine its precise location based on signals received from a constellation of US military satellites.