Ephemeris refers to data that describes an object’s position over time. Ephemerides is the (plural) form of Ephemeris. In MaxQ/SPICE Ephemeris data is stored-in/loaded-from SPK Kernel files.

Ephemeris data can be used to compute position and state vectors for objects that have sufficient data via SPK Kernels.

This is the preferred method for positioning as it is generally the most accurate. Given good data, SPICE’s accuracy can be on the order of two centimeters for space probes that have left the solar system, such as the Voyager probes.