IAA, or in-app advertising, is a revenue stream for mobile apps that seek to leverage the app’s real estate to show ads to users. In other words, ad buyers spend in order to display ads within the app.
IAA is a popular monetization strategy for app developers looking to create a revenue stream by selling real estate in their apps to other advertisers.
The way it works is by developers integrating an SDK to connect to an ad network, and implementing user-friendly ad units – earning revenue when users interact with the ads.
The mobile app ads are then served through an advertising network, which connects advertisers and developers. The app requests an ad from the network, and the network uses algorithms to identify and deliver the highest paying ad to the user in real time.
Source: Unity Technologies Blog