Google AdSense is a program that allows website owners the possibility of additional revenues by displaying ads targetted to an audience. (Ex. handbags may target women). These adverts are administered, sorted, and maintained by Google, and generate revenues by either a per-click or per-impression basis. This money is shared by Google to the respective website owner.

• Pay Per Click - advertisers pay the publisher (typically a website owner) when the ad is clicked.
• Per Impression or (Cost Per Impressions) advertisers pay for every time an ad is displayed

This works for both Google and FaceBook