Zener diode working as a voltage regulator explains it

The term regulator means which regulates or controls, Zener diode can work as a voltage regulator if it is introduced in a circuit. The output across the diode will be constant. It is driven by a current source. As we know if the voltage across the diode exceeds a certain value it would draw excessive current from the supply. The basic diagram of zener diode as voltage regulator is given below,

To limit the current through the zener diode series resistance R is introduced whose value can be chosen from the following equation

Resistor value (ohms) = (V1- V2)/(zener current +load current ) 

The above diagram is of a shunt regulators because the regulating element is parallel to the load. The zener diode produce a stable reference voltage across the load which fulfills the criteria of regulator.