viewable impression - A viewable impression is a digital marketing metric that counts only the ad impressions that are actually seen by a user, defined by industry standards (MRC/IAB) as at least 50% of the ad area being visible on screen for at least one continuous second. Unlike served impressions, which only track if an ad was loaded, viewable impressions ensure that the advertisement had a genuine opportunity to be seen, making it a critical metric for campaign ROI and preventing wasted ad spend.
