What does ephemeris mean?

in astronomy and in the celestial navigation, the word Ephemeris projects the the trajectory of naturally occurring objects (in an astronomical sense), it also covers artificial satellites in the sky. that also means the position (possibly velocity) over time.

Error in the ephemeris content

This error is in fact the difference between the actual position of the satellite and the expected position. As your GNSS receiver uses the satellite’s position to calculate its own position, small errors in the orbit can have an effect on the accuracy of your GNSS antenna.

This can occur when the satellites orbit changes, the ground control system then sends a message to the satellite updating the contents of the ephemeris that was broadcasted.