Percentage of measured impressions that are seen by a user. This is an important metric, especially for brand advertising, because if an ad cannot be seen, it cannot influence the consumer. The industry uses the standard Media Ratings Council (MRC) definition, which is that display or video ads have 50% of pixels displayed on screen for 1 second or more. Viewability can be priced as a viewability goal or a viewability guarantee, with the latter priced as a vCPM (or “viewable” CPM). Viewability reporting provides percentages on “in-view,” “out-of-view,” and “non-measured” impressions. To better understand “non-measured” impressions, please see dark viewability.