is an online advertising service operated by Google
that as only applicable for Smartphone applications. There are three types of ads in Admob. Each ad type is simply called an ad unit:
1) Banner Ads
2) Interstitial Ads
3) Reward Video Ads
Admob allow developers to generate money from their apps. It is available both for Android & iOS platform. When you start using Admob, you have total control what type ads you want to display in your app. Revenue is generated when a specific amount of impressions are generated or when the user clicks on the ad.
You can learn more about Admob at Admob Official Site