What is CPM (Cost Per Thousand)?

The practice of calculating a cost per 1000 ad displays. It is used by programs that pay on an impression basis -- with the CPM rate being the amount you earn for every 1000 times an advertisement is displayed. For example, a $5 CPM means you earn $5 every time 1000 ads are displayed on your site. CPM can also be calculated for pay-per-sale, pay-per-lead and pay-per-click programs by using this formula:

Amount earned / (number of impressions/1000)