When an advertisement is viewed, it creates an impression, which is a total gross count of advertising exposures.
In other words, impressions count an individual each time he or she sees the display, so it includes multiple exposures by the same individual.
One person can produce more than one impression based on the number of times they see the ad. Therefore, if an ad achieves 100 impressions, that doesn't mean it's seen by 100 people. It has duplication and could be reaching only a few people, multiple times.
While impressions as a basic audience measurement is comparable across most media types, there are nuances in the way an impression is "counted" by media format. For OOH, we have relined our impressions to those "likely" seen versus just an opportunity to see through visibility factors based on a location's individual characteristics.
Impressions are an important metric and are the foundational media currency of OOH which means they can be compared and added across channels if the universe base, both demographically and geographically, is consistent.
In summary,
--The fundamental gauge of advertising exposures is provided by impressions, which encompass repeated views and are a widely-used metric across all ad formats.
--The number of impressions does not represent the number of individuals who have viewed the advertisement; rather, it reflects the total count of all exposures.