According to the geocentric Ptolemaic system, planetary orbits have two components: a circular or deferent orbit around the parent body; and a smaller circular orbit, or epicycle, around a point on the deferent orbit.

The deferent is the large circular orbit around which a planet was thought to orbit, in one or many epicycles.

Epicycles are circular orbits within orbits that were used to (incorrectly) describe the orbits of objects in the Ptolemaic system (about A.D. 150).

Epicycles and deferents were used to predict orbits until Kepler discovered the elliptical nature of orbits (early in the 1600's).