What is In-app Billing ?
In-appproducts are the digital goods that you offer for sale from inside your Android application to your app users. You cannot use In-app Billing to sell personal services, physical goods, or anything that requires physical delivery.
The Version 3 API supports managed in-app products and subscriptions to give you flexibility in how you monetize your application. You can specify these types of products by using the Google Play Developer Console.
Managed in-app products:
When a managed in-app item is purchased by an user, Google Play stores the purchase information for each item on a per-user basis.