PPC stands for Pay Per Click and RPC stands for Revenue Per Click. If you were promoting a PPC offer, Pay Per Click means that you would get paid each time a user clicks on your ad or sponsored link. It’s by far the fastest way to earn money, however, the amount you would typically earn per click is comparatively low when compared to CPA or Revshare payouts, which are better for the long term relationship you have with the adult affiliate programs you work with. Pay Per Click is typical for advertising networks, not for affiliate programs, but some do offer it. Good luck!