Zener diode works as normal diode in forward direction but it also allows current to flow in the reverse direction (reverse breakdown region) when the voltage is above certain value. This voltage value is known as Zener voltage and is distinctive for that particular type of Zener diode. This behavior of Zener diode is widely used to make voltage references for voltage regulators, as shunt regulators and to protect other semiconductor devices in circuit from momentary voltage pulses.