An 'Ad Impression' in digital advertising is counted each time an advertisement is fetched and displayed to a user, regardless of whether it is clicked or not. This metric is vital for understanding the reach and frequency of an ad’s visibility.

Tracking ad impressions helps advertisers gauge the exposure of their ads across platforms and audiences. It is an essential metric for assessing the initial step in the advertising effectiveness, preceding engagement and conversion metrics.

High ad impressions can indicate a wide reach, but the true measure of an ad's success also includes engagement and conversion. Advertisers analyze impressions alongside other metrics to optimize their campaigns and ensure maximum return on investment.