Definition & Explanation

An impression is a single instance of an ad being served to a user’s device, whether on desktop, mobile, or connected TV. Each time an ad loads and is delivered, one impression is counted—though this does not guarantee the user actually saw or engaged with the ad. Viewable impressions and verified impressions are more refined metrics that account for actual visibility and fraud filtering. Advertisers use impression counts to evaluate reach and calculate cost per mille (CPM).