This document discusses zener diodes and their use in voltage regulation circuits. It defines key characteristics of zener diodes including zener voltage (VZ), which can range from 2V to 200V depending on the diode. Zener diodes are constructed to withstand the zener effect or avalanche breakdown that occurs at VZ, dissipating power without damage. The document provides examples of using zener diodes in simple voltage regulator circuits to maintain a stable voltage across a load resistor.