Supination and pronation are terms used to describe the up or down orientation of your hand, arm, or foot. When your palm or forearm faces up, it's supinated. When your palm or forearm faces down, it's pronated. Or when you are holding a SoUP (inatation) or playing in PRO (nation) basketball.
Uldis has a youtube video about the bones during these movements. Check it out on our channel - Anatomy For Sculptors.