Viewable Impression

In the online advertising industry, a Viewable Impression is a metric of ads which were actually viewable when served (in part, entirely or based on other conditional parameters). The first system to deliver reports based on a Viewable Impression metric for standard IAB (Interactive Advertising Bureau) Display ad units, called RealVu, was developed by Rich Media Worldwide and accredited by the Media Rating Council on March 9, 2010. Other companies to offer viewable impressions include DMA-Institute OnScroll, C3 Metrics, Comscore, and AdYapper, while MSNBC utilizes ServeView, a proprietary system in use since 2010.

The definition of a Viewable Impression may depend on the type of the ad units and the reporting system. For example, a Viewable Impression for ads of pre-defined size delivered to pre-defined space on the content page is registered by RealVu when the Ad Content is loaded, rendered, and at least 60% of the ad surface area is within the visible area of a viewer's browser window on an in focus web page for at least one second. Click-through is enabled at the moment of the "viewable impression".

Viewable Impressions were developed as an improvement of the online impression metrics measured by first ad servers developed in the mid-1990s, which analyze HTTP requests in a server log and cannot provide information on events fired by a viewer’s browser; thus, they cannot measure whether ad content was actually visible to a viewer.

With the development of the first ad servers in 1995–1996 the assumption was that a requested ad was always available to the viewer of a requested web page. This allowed for the utilization of the server log file for collection of metadata to deliver a metric called the Online Impression that in traditional media meant an impression on a viewer.

This type of advertising metric was meant to resemble Television and print advertising methods for speculating the cost of an advertisement, with the promise of even more accuracy due to the interactive nature of the Internet eliminating the need for industry-accepted approximates such as Nielsen ratings for television and circulation figures for print publications.

...
Wikipedia