This is a technology that utilizes a series of satellites that transmit signals, enabling GPS receivers to determine a location. GPS is used as a generic term to refer to this technology even though the Global Positioning System is the only completed system and developed by the United States. Other systems in development like the Galileo positioning system, in Europe, will provide similar technology.
GPS receivers are commonly used for navigation commercially in airplanes, ships, etc. For consumers GPS receivers are used often for street navigation in cars and for hiking.
