Google Keyword blog: Optimizing App Monetization with Google AdMob

… It is a component based ad format that matches the look and feel of the app where the ad is being displayed. This makes the ads look like they are a part of the app and reduces obtrusiveness. A simple example of this is a promoted tweet on Twitter or a promoted post on Facebook. It is essentially a tweet or post like any other, but an identified sponsor has paid to promote it.