Final answer:
Forearm pronation is a movement that rotates the palm to face downward or posteriorly, contrasting with supination, which rotates the palm to face upward or anteriorly.
Step-by-step explanation:
A movement that turns the palm to face posteriorly or downward is referred to as forearm pronation. This motion moves the palm from the palm forward or supinated position to the palm backward or pronated position. In the pronated position, the radius crosses over the ulna, creating an "X" shape when viewed from above. This is different from supination, which turns the hand back to the palm forward position, where the radius and ulna are parallel.