What is an ad impression?
An ad impression is counted whenever an ad is displayed within an app.
Ad impressions vs clicks should not be confused with each other. In other words, impressions in digital marketing tells advertisers and developers how many times an ad was viewed by users. The ad impressions definition is not contingent how many times the ad was clicked.
App developers get paid for every 1,000 ad impressions, which is measured by eCPM.