[O.B.Left]

Swiveling occurs when the Clubface (Left Wrist) changes from Vertical to On-Plane and back to Vertical again.

Thanks D.

Id personally would just say Left Hand above.

The clubface given what Homer termed Grip Rotation may or may not align to plane at Top , may or may not be vertical at Low Point. May or may not be parallel to the left arm at the top of the backswing as is commonly held. But ideally the Left Hand lays flat to plane at top. My right palm lays flat to the bottom of the plane too. But I have a vertical/vertical grip type. As I assume you must.