Final answer:
Supine refers to the position of lying on the back with the face upwards. The safety belt should be placed across the lap and lower anterior torso without impeding circulation.
Step-by-step explanation:
The term 'supine' refers to the anatomical position where the person is lying on their back with their face upwards. In the context of safety belts, the term refers to the placement of the belt across the lap and lower anterior torso, while not impeding circulation. This means that the belt should be positioned low on the pelvis, across the hips, and snugly fitted without causing discomfort or restricting blood flow.