Final answer:
The area not seen in the vehicle's mirrors is known as a blind spot, which is a critical area for driver safety to be aware of when making decisions on the road.
Step-by-step explanation:
The area to the rear of the vehicle not seen in mirrors is a blind spot. This is a zone around the vehicle that cannot be directly observed by the driver while at the controls, under existing circumstances. It is important for driver safety to be aware of blind spots and to check them by briefly looking over their shoulder before changing lanes or making maneuvers in traffic.