Ephemeris refers to the orbital data that the satellite transmits for that satellite and for every other satellite in the GPS system. This data can be in the form of the broadcast ephemeris as extracted from the navigation message, or in form of the precise ephemeris as determined by the International GPS Service(IGS).

For GPS use, ephemeris data includes the relative health of the satellite, its position, relationship to other satellites, and calculations of signals to the ground. The combination of this information can be used to determine the positional accuracy of the signal so that receivers on the ground can more accurately determine their positions.