Definition of "precession"

(uncountable) Precedence.  examples

(physics, countable) The wobbling motion of the axis of a spinning body when there is an external force acting on the axis.  examples

(astronomy, uncountable) The slow gyration of the earth's axis around the pole of the ecliptic, caused mainly by the gravitational torque of the sun and moon.  examples

Any of several slow changes in an astronomical body's rotational or orbital parameters.  examples