Ad Impression

Detailed explanation

An Ad Impression is recorded every time an ad unit is served and rendered on a user's screen, regardless of whether the user notices it, engages with it, or scrolls past it. It is the most basic countable event in display, video, and social advertising, and it forms the denominator for foundational pricing and performance metrics like CPM (cost per thousand impressions) and CTR (click-through rate).

Because an impression only confirms that an ad was served, not that it was actually seen, the industry has layered additional standards on top of raw impression counts — viewability (whether a meaningful percentage of the ad was actually in the visible browser viewport) and verified/valid impression filtering (removing bot or fraudulent traffic) are now standard requirements in most media buys, since a served-but-invisible impression provides little real value to an advertiser.

Ad impressions are typically reported alongside reach and frequency: reach shows how many distinct users were exposed, and frequency shows the average number of impressions each of those users received, which together tell a media planner whether a campaign is spreading efficiently or over-saturating a smaller audience.