InappPurchase

In-app products are the digital products that you offer for sale to users from inside your application. Examples of digital products include in-game currency, application feature upgrades that enhance the user experience, and new content for your application.

You can use In-app Billing to sell only digital content. You can't use In-app Billing to sell physical products, personal services, or anything that requires physical delivery. Unlike with priced applications, there is no refund window after the user has purchased an in-app product.