Rotation of the forearm so the palm faces down (pronation) or up (supination), which is what separates an overhand grip from an underhand one.
Supination is the position that carries a bowl of soup. Pronation is the position of a pull-up, a barbell row and a standard bench press grip.
Grip position changes which muscles do the work. A supinated curl loads the biceps hardest because the biceps is also a supinator; a pronated reverse curl shifts the load to the brachioradialis and the forearm extensors. Running both, three sets of 10 supinated and two sets of 12 pronated, covers the arm better than five sets of one.
At the foot, the same words describe the ankle rolling inward or outward, which is where most people meet them when buying running shoes. The two uses are unrelated in the gym.