1. A diode in which the voltage is independent of the current for a considerable range of current values; such as, a Zener diode or a two-terminal semiconductor junction device with a very sharp voltage breakdown as a reverse bias is applied.

The diode may be used as the main component of a simple voltage regulator, or as a constant voltage reference for a more elaborate voltage regulator circuit.

2. A diode that maintains an essentially constant direct voltage in a circuit despite changes in line voltage or load.