Impression

Impression or impression, is a unit of the emergence of an ad banner on a web page accessed. Advertisers use impressions to measure the amount earned by the view their ads, and publishers will sell ad space according to the number of impressions generated.

It is rather difficult to determine, whether an impression really means that a visitor has seen these ads or not, because they can only do browsing without images or did not scroll far enough down, so ads become invisible. Impressions are tracked by using a log that continues to be recorded by the server. Another way to determine the price of an ad banner is to use CPC, or cost-per-click.