Peak Inverse Voltage

Pick inverse voltage(PIV)

The Peak inverse voltage (PIV) equals the peak value of the input voltage, and the diode must be capable of withstanding this amount of repetition reverse voltage. For the diode in figure, the maximum value of reverse voltage, designated as PIV, occurs at peak of each positive alternation of the input voltage when the diode is forward biased.
Or simply ~  Peak Inverse Voltage (PIV) or Peak Reverse Voltage (PRV) refer to the maximum voltage a diode or other device can withstand in the reverse-biased direction before breakdown. Also may be called Reverse Breakdown Voltage.

Importance of PIV

Typically this is the maximum reverse polarity voltage that can be applied to a diode before it starts to break down and conduct current.  Diodes always have a reverse leakage current, although usually very small for rectifier diodes (100nA - 500uA would be typical), so the reverse voltage specification is the voltage at which the diode conducts a defined amount of current in the reverse direction.