Viewable impression is an online advertising metric that indicates whether an online ad is visible and has been seen by users.
The viewable impression metric is defined by the Interactive Advertising Bureau( IAB) and indicates that at least 50% of the pixels on a browser page are displayed for at least one second. Since online advertising is often not seen due to ad blockers, placement or too short call-up times, but has to be paid for, the key figure visible impressions determines whether the user has actually seen the online advertising.
Visible impressions depends on the type of online advertising, the size of the banner, its positioning, rendering and many other factors. Once the visible impressions are detected, they activate the click-through rate.