According to Wikipedia:
Precession is a change in the orientation of the rotational axis of a rotating body.
Lets use the example of a top:
The Precession Circle is the circle that the top moves around as it spins. Because of irregularities in the spin, gravity applies a torque to the top and pushes it down, causing precession.
Angular Momentum and Angular Velocity
The top rotates because of Torque due to Angular Momentum.
