Ship motion is generally expressed in six degrees of freedom, which can be regarded as combinations of :
three oscillations about horizontal or vertical axes :
roll, pitch, and yaw
and three linear displacements of the center of gravity:
heave, surge, and sway
describes the "sliding" lateral, side-to-side motion of a ship.
describes the vertical, up (scending)
and down (descending)
motions of the hull.