PRONATION: movement of the palm of the hand from an anterior or upward-facing position to a posterior or downward-facing position. This action moves the distal end of the radius across the ulna. (There is NO rotation of the arm: the arm is immobile during pronation)

SUPINATION (the reverse of pronation): movement of the palm from a posterior position to an anterior position. During supination, the radius and ulna are parallel.