Cold air carrying body heat away from the body is best defined as:

The scenario described involves cold air moving around the body and causing heat loss, which is best defined as convection. Convection refers to the process of heat transfer through the movement of fluids, including liquids and gases. In this case, the cold air acts as a medium that absorbs heat from the body as it moves over the skin, effectively cooling the body down.

This mechanism is particularly relevant in outdoor environments, especially in windy conditions where air movement can significantly enhance heat loss from the body, leading to a rapid decrease in body temperature. By understanding convection, EMTs can better assess and manage cases of hypothermia or heat loss in patients exposed to cold conditions.