Answer:
Precession: The slow movement of the axis of a spinning body around another axis due to a torque, such as gravitational influence, acting to change the direction of the first axis.
Barycenter: The center of gravity between two objects
Nutation: As an object precesses, it will not precess in a circular path, but will wobble/ oscillate slightly. This wobble is nutation, the periodic movement of an axis due to gravitational interactions with other bodies.
These are all caused by gravitational interactions between two or more bodies.