What does XX/YY/ZZ exactly stands for

I often read that players are referred as tight or loose and aggressive or passive by three figures VPIP/PFR/Aggression and I'm not sure about the last number. When I'm using PokerTracker oder Poker Office, does Aggression mean Total Aggression or Aggression PostFlop since the aggression pre flop is already indicated with the PFR number. So what does aggression or the number really mean?

Thanks for the help

AF measures aggression over all streets not just the pre flop. Here's how it's calculated: -

(total times bet + total times raised)/(total times called)