A 2-terminal semiconductor, and subset of the diode family, that exhibits a stable voltage over a wide range of currents passing through it, creating a constant-voltage characteristic. Zener diodes are commonly used in power supply reference circuits.
When connected in parallel with a variable voltage source (reverse-biased), a zener diode acts as a short circuit when the voltage reaches the diode’s reverse breakdown voltage, and therefore limits the voltage to a known value. A zener diode used in this way is known as a shunt voltage regulator (shunt meaning connected in parallel, and voltage regulator being a class of circuit that produces a fixed voltage).