CPM stands for "Cost Per Mille," which is a marketing term that refers to the cost of reaching one thousand impressions or views of an advertisement. It is commonly used in online advertising to measure the effectiveness and cost-efficiency of ad campaigns. Advertisers use CPM to determine how much they are willing to pay for their ads to be displayed to a large audience. Calculating CPM is straightforward: you divide the total cost of the ad campaign by the number of impressions (in thousands). For example, if an ad costs $500 and receives 100,000 impressions, the CPM would be $5. This metric helps advertisers compare different advertising options and optimize their budgets.