If someone has proof or first-hand knowledge about an app violating Facebook's terms of service by collecting and transferring people's data to another party, whether for money, political influence or scams, they can notify Facebook through this program. If the tip pans out, Facebook will "shut down the offending app and take legal action against the company selling or buying the data, if necessary." The person who reported the tip will also get paid: The reward could be as high as $40,000, though Facebook notes that there is no maximum payout.
You can check out the Data Abuse Bounty Program on Facebook, but it's not a surprise that Facebook would turn to its users to help police the social network. It's proven to be too big and complex for Facebook' security to handle, and while the company is increasing the number of employees it has to monitor the service, incentivizing its user base to report on these issues makes a lot of sense.