Avalanche effect:

Greater the reverse bias voltage, more determined an insulator P-N junction gets-to a point. If reverse bias goes past this critical value, the voltage overcomes the ability of junction to prevent the flow of current, and junction conducts as if they were forward biased.  This avalanche effect does not ruin junction (unless voltage is extreme);  it is a temporary thing. When voltage drops back below the critical value, the junction starts behaving normally again.

Some of the components are designed to take the advantage of the avalanche effect. In the other cases, avalanche effect limits performance of the circuit. In a device designed for the voltage regulation, called as Zener diode, you will hear about avalanche voltage or Zener voltage specification. This might range from the couple of volts to over 100 V. It is significant in the design of voltage regulating circuits in solid state power supplies.

For rectifier diodes in power supplies, you will hear about peak inverse voltage (PIV) or peak reverse voltage (PRV) specification. It is essential that the rectifier diodes have PIV great enough so that the avalanche effect will not occur during any part of the alternating current cycle. Else, the circuit efficiency will suffer.