In-app purchases are virtual goods users buy within apps, such as in-game currency, recurring subscriptions, and more. There are various types of in-app purchases: content which users pay to unlock new levels and features; upgrades such as new characters or gear; and currency which are purchased in bulk to extend app use.
In addition to mobile app advertising, in-app purchases are used by app developers as an app monetization strategy. The best strategies combine both. For example, game developers often integrate ad units such as rewarded videos as a way to increase in-game purchases.