Cost per thousand impressions.
It is advertising bought on the basis of impression.
The total price paid in a CPM deal is calculated by multiplying the CPM rate by the number of CPM units. For example, one million impressions at $10 CPM equals a $10,000 total price.
1,000,000 / 1,000 = 1,000 units
1,000 units X $10 CPM = $10,000 total price
The amount paid per impression is calculated by dividing the CPM by 1000. For example, a $10 CPM equals $.01 per impression.
$10 CPM / 1000 impressions = $.01 per impression