Impression

An impression is one opportunity for a person to see an ad. Every time an ad is shown and someone could have seen it, that counts as one impression. It is the basic counting unit of advertising, and the basis of CPM pricing.

The word means something slightly different depending on the medium. Online, an impression usually means the ad was loaded on one person’s screen. In out-of-home, one play on a public screen can generate many impressions at once: one for each person passing by.

Because nobody clicks a billboard, out-of-home impressions are estimated: measurement bodies combine traffic counts, mobility data and the screen’s characteristics to calculate how many people had a real opportunity to see each play.