A Zener diode is a special type of semiconductor device that allows current to flow in the reverse direction when a specific voltage, known as the Zener voltage, is reached. It is designed to operate in the breakdown region, where it can maintain a stable output voltage despite variations in the input voltage or load conditions. This makes it useful for voltage regulation in electronic circuits. Zener diodes are commonly used in applications such as voltage regulation, surge protection, and reference voltage sources. They are often found in power supplies and other electronic devices where maintaining a consistent voltage is crucial. By using a Zener diode, engineers can ensure that sensitive components are protected from voltage spikes and fluctuations.