1. The fact of going in front of something as in a line up, personal importance, etc: The precession of the guests of honour at the banquet was written out for the wait staff to understand.
2. In astronomy: the slow, conical motion of the earth's axis of rotation: Precession is caused by the gravitational attraction of the sun and moon, and to a smaller extent, of the planets, on the equatorial bulge of the earth.

In certain contexts, precession may refer to the precession that the Earth experiences, or the effects of this type of precession on astronomical observation, or to the precession of orbital objects.

In physics, the movement of the axis of a spinning gyro in orbit around a heavenly body which is caused by the curvature of space: Geodetic precession describes the curvature of spacetime, predicted by general relativity, on a vector carried along with an orbiting body.