"sway" is an inclination of the body produced by the stretching of one
side of the body or the other. A promenade sway is a left sway
performed in promenade or semi-closed position. We step down line on
the lead foot and stretch up and over the lead wrists. Right side
stretch (left for the woman) both leads the opening into semi position
and produces the sway.
Notice how "up" the bodies are in a promenade sway.
The forward poise is especially strong here.
Usually, the choreographer allows us to linger in a promenade sway; it is a nice "picture figure."
From the back, we can recognize the strong frame. The arms are up, the bodies are stretched, the chins are high.