The alternator belt is a belt that transmits the engine's rotational energy to the alternator. It wraps around a complex pulley connected to the crankshaft. As the engine starts and the crankshaft rotates, the belt moves as well, transferring rotational energy to the alternator. The alternator, which is a type of generator, converts this energy into electricity to charge the battery and supply power to various parts of the vehicle.
Although the primary function of the alternator belt, as its name suggests, is to transfer the engine's rotational power to the alternator, in modern vehicles, both the timing belt and this belt also drive other engine components such as the water pump, power steering pump, oil pump, air conditioning compressor, and more.