GPS is the abbreviation for "Global Positioning System" - a satellite-based navigation system, which was originally developed for military purposes. Since many years, GPS is also available for civil use and the neccessary devices are also affordable for private users. Normally an accuracy of less than 10 meters is possible, with good reception conditions even less than 5 meters.

If you want to know more about the details, please have a look at Global_Positioning_System.

These pages are mainly about the practical usage of GPS.