The movement of an object, or celestial body, along a circular path (epicycle): 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 also called an epicycle motion, 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 150 A.D.

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