How does Pay per Impression work?
An impression is the display of an ad to a user while viewing a web page. A single web page may contain multiple ads. In such cases, a single page-view would result in one impression for each ad displayed. In order to count the impressions served as accurately as possible and prevent fraud, an ad server may exclude certain non-qualifying activities such as page-refreshes or other user actions from counting as impressions. When advertising rates are described as CPM or CPI, this is the amount paid for every thousand qualifying impressions served at cost.