I take it to mean an earth/moon/sun orrery that demonstrates the relative motion of the earth and moon around the sun.
A tellurion can show the earth's seasons .
Moon and sun eclipses can be demonstrated and with an accurate tellurion it may be possible to predict the timing of moon and sun eclipses and what type of eclipses they are i.e. whether solar eclipses are total or annular.
A tellurion can also help explain the reason that only one tide per day is experienced in some parts of the earth.
You will see some tellurions listed in both the Orrery list and the tellurion list