GPS is an acronym for "Global Positioning System." The 1st GPS satellite was put into space in 1978.   GPS satellites send signals to GPS receivers on the ground.  There are at least 24 satellites working at any one time. When the signals from at least three GPS satellites have been received, the receiver is able to pinpoint location very precisely.  This is expressed in longitude and latitude coordinates, such as 45 degrees North and 100 degrees West.