Final answer:
When a driver's hand arm is straight out, it refers to the anatomical position where the elbow is fully extended and the palms are facing forward. This position allows the forearm and hand to swing freely or carry objects without hitting the hip.
Step-by-step explanation:
In biology, when a driver's hand arm is straight out, it refers to the anatomical position where the elbow is fully extended and the palms are facing forward. In this position, the forearm deviates laterally by 5-15 degrees from the line of the arm, forming a carrying angle. This angle allows the forearm and hand to swing freely or carry objects without hitting the hip. The carrying angle is larger in females to accommodate their wider pelvis.