Scull: the continuous movement of the hands in the water to support and balance one's body.

Swimmers use their arms and hands to scull through the water; this method of propulsion provides a surprising amount of speed and accuracy of direction, considering there’s no kicking involved, and a complete absence of splashing. This combination of attributes makes sculling a popular mode of locomotion for synchronized swimmers. There are three basic sculls used in synchronized swimming:

Hip scull

The basic hip scull can be used to move one’s body through the water as it floats (face up) on the surface. Arms are held at the sides, elbows close to the body; the hands move, fingers together, in a figure-eight pattern as though smoothing sand at the beach. If the fingers are up, “waving” at the feet, the body will move headfirst through the water; if the fingers are down, hands slightly cupped, the body will move feet-first. By pulling (or pushing) unevenly—harder with one hand than the other—one can cause the body to turn, or correct for unwanted turbulence caused by the motion of the water.

Overhead scull

The overhead scull can also be used to move head- or feet-first through the water, while floating in a face-up position. To move headfirst, extend arms overhead, hands slightly cupped, and weave arms toward and away from each other. (This always felt like an Egyptian dance move to me…) To move feet-first (a move known as torpedo), turn palms out, away from the head, thumbs toward each other, and wave in a figure-eight pattern at the receding pool wall behind you.

Support scull

The support scull is used when the feet ( toes pointed!) and legs are out of the water and the head is pointed toward the bottom of the pool; the elbows are at the waist, and the lower arms and hands are extended out in front of the body. The motion, again, is a figure-eight, as though smoothing a tablecloth on a table at waist height, except the palms are pushing toward the pool bottom. Done correctly, this scull provides enough support to keep the lower half of the body raised above the surface of the water.

Sources: . . . And four years of synchro in college; I found it amusing that, as I tried to write this, I had to rely on kinesthetic memory; my body remembered the moves when my brain did not.