Peak inverse Voltage 

Peak  inverse voltage is   important parameter in the design of rectifier circuit. PIV is the maximum  voltage that appears across the device  during its blocking state. Hence it is applied to the SCR in the reverse direction. It is the amount  of voltage  the SCR can withstand in the reverse direction without  having  current  flow.

Gate  trigger current: The  maximum  value  of gate  current  required to switch  the device from  the off state  to the  on  state under  specified conditions. The  designer should consider  the maximum  gate trigger current  as the minimum trigger current  value  that must  be applied  t the device in  order  to assure its proper triggering.