World Geodetic System 1984 (WGS84)
The World Geodetic System 1984 (WGS84) is the datum used by the Global Positioning System (GPS). The datum is defined and maintained by the United States National Geospatial-Intelligence Agency (NGA). Coordinates computed from GPS receivers are likely to be provided in terms of the WGS84 datum and the heights in terms of the WGS84 ellipsoid.
A technical description of the WGS84 datum is provided on the NGA website.