Engagement rate is the ratio of engaged users to active users of an app. It refers to the users who engage actively with the ads on the app.
Engagement rate = engaged users/total active users.
The engagement rate is important to determine the performance of the app. It also measures the effectiveness of ad unit placement, especially for rewarded ads.
Engagement rate also helps determine the overall revenue of an app and keep track of unique users who engage with in-app ads as these users generate revenue for the marketers.