The correct answer is B) sway. Sway refers to the horizontal transverse motion of a vessel, which is the side-to-side movement of the ship along its beam or width. This motion is one of the six degrees of freedom that a vessel experiences, the others being surge (forward/backward), heave (up/down), roll (rotating around the longitudinal axis), pitch (rotating around the transverse axis), and yaw (rotating around the vertical axis). The other options are incorrect because heave is the up-and-down motion, surge is the forward and backward motion, and pitch is the rocking motion around the transverse axis.