In App Purchase

Anyone had Idea what is In App Purchase?
How does it help in earning


In app purchase you can sell some more item/ unlock some level in your free game/app by taking some amount from users.In the free game/app you can implement that to gain money.It help to sell your app/game more rather than a paid game.

About in-app purchases. Many iPhone, iPad, iPod touch, and Mac apps allow you to buy subscriptions or extra content (such as in-game currency, a full game unlock, or bonus content) in the app.