Facebook will sell ad inventory on third-party sites and target it using its own data AND third-party data.

Google AdSense does about $2.5 billion in revenue per quarter; so, FaceSense could be worth $10 billion figure.

Read more: http://www.businessinsider.com/a-plugged-in-ad-tech-source-drew-this-diagram-to-explain-facebooks-next-10-billion-business-2012-7