Sway

Sway is the soft lean of the body to one side, used mostly in the smooth dances to balance the momentum of a turn or a travelling figure. When a couple curves across the floor, a little sway keeps them poised over their feet instead of being thrown off balance, and it adds the long, elegant line that makes ballroom look the way it does.

It is a whole-body inclination from the feet up, not a bend at the waist, and it works together with rise and fall to give figures their shape. Too little sway looks stiff; too much looks like leaning. The right amount usually appears on its own once your frame and rise are steady.