OP can either me "Over-Powered" As in "Omg name Is soooo OP"
or Original Poster aka "OP is dumb close thread"
Zerk is when a thing like god of frenzy or sacrificial slash activates. Zerk crit means the activation crits.
Proc rate means chance of a meelee stone/status activating. AKA god of frenzy, Thunder strike, Sacred stones etc etc