The part at the back of the hip, which, in man, forms one of the rounded protuberances on which he sits; the rump. Often used in the plural -- see buttocks.

either of the two large fleshy masses of muscular tissue that form the human rump

This is the curve created by intersecting a plane at a specific half-breadth (Y-value) with the hull geometry. The curve can be seen in the profile view of the boat.

The intersection of the molded surface of the hull with any vertical longitudinal plane not on the centerline.

The convexity of a ship behind, under the stern.