The reference Earth model used by the Landsat 7 system.

a consistent global coordinate system which allows an unambiguous representation of positional information

A consistent set of parameters describing the size and shape of the Earth, the positions of a network of points with respect to the center of mass of the Earth, transformations from major geodetic datums, and the potential of the Earth (usually in terms of harmonic coefficients).

defines the current U.S. DoD standard horizontal and vertical reference datums for a geodetic coordinate system, collected and standardized in 1984.

The World Geodetic System defines a reference frame for the earth, for use in geodesy and navigation. The latest revision is WGS 84 dating from 1984 (last revised in 2004), which will be valid up to about 2010.