Back EMF in motors is the voltage generated in the windings when the motor operates, opposing the applied voltage due to the motor's rotation and magnetic field. It plays a crucial role in regulating motor speed and preventing excessive current draw, acting as a safety mechanism. The distinction between EMF and potential difference (PD) is that EMF refers to energy conversion per unit charge, while PD is the energy converted into other forms. Without back EMF, motors could spin uncontrollably and risk burnout. Understanding back EMF is essential for grasping motor functionality and safety.