Why breakdown diode is called so?

A breakdown diode is called so because it operates in the breakdown region of its voltage-current characteristic curve. In this region, a small increase in voltage can lead to a large increase in current, allowing the diode to conduct in reverse bias. This behavior is typically utilized in applications like voltage regulation and clamping, where the diode prevents excessive voltage from damaging other components. The name reflects its ability to "break down" and conduct under certain voltage conditions.