The oversway is something of an opposite to the promenade sway. We step side on the lead, but we soften that knee instead of stretching up, and the man stretches the left side instead of the right, thus closing the woman's head and moving to a closed position, rather than semi-closed. The figure is finished with a little left face body rotation.
You can perform the oversway by itself, but more often, you will be asked to do a promenade sway and then to change to an oversway, or simply "change the sway."
The promenade sway is a left sway down line. Changing from right-side stretch to left-side stretch changes the left sway to right sway and the semi-closed position to closed position. Again, a little seasoning is added to the dish in the left- face body rotation and extension of the upper body.