Zener breakdown is a phenomenon that occurs in semiconductors when a reverse voltage applied across a diode exceeds a certain threshold. At this point, the electric field becomes strong enough to pull electrons from their valence bands, allowing them to conduct electricity. This process is useful in regulating voltage in electronic circuits. In Zener diodes, this breakdown is intentional and occurs at a specific voltage, known as the Zener voltage. When the voltage exceeds this level, the diode allows current to flow in the reverse direction, maintaining a stable output voltage. This property makes Zener diodes essential for voltage regulation and protection in various electronic applications.