Viewableimpression
Viewable impression is a digital advertising metric indicating that an impression had a reasonable chance to be seen by a user. It represents a subset of all served impressions, filtered by a standard for what counts as “in view.” The concept is used to assess how much of an ad actually appeared on a user’s screen long enough to be noticed, rather than merely being loaded.
Industry standards for viewability are defined by the IAB Tech Lab in collaboration with the Media Rating
In practice, viewable impressions are used to price and optimize campaigns, with metrics such as viewable CPM