Nutation occurs when a spinning gyroscope that is balanced at its centre of gravity is given an additional angular momentum. This additional angular momentum will give a new angular momentum vector which does not correspond with the axis of symmetry.
Although the gyroscope is still spinning with angular frequency , the axis of symmetry is now itself rotating with an angular frequency , an effect called nutation the relation between the nutation speed and rotation speed depends on the different moments of inertia relative to the principal axes of rotation.