The correct answer is B) yaw. When a tow veers to the side on the end of the towline, this motion is referred to as "yawing." Yawing is the rotational movement of the towed vessel around its vertical axis, causing it to swing from side to side. This is a common phenomenon in towing operations and is an important consideration for maintaining control and stability of the tow. The other options are incorrect because they describe different types of motion: A) sway refers to lateral movement, C) surge refers to forward/backward movement, and D) swing refers to a more general side-to-side motion, which is a broader term than the specific "yawing" motion.