Floor CPM, or cost-per-mille, is a pricing model used in the online advertising industry that sets a minimum price for ad impressions. CPM is calculated by dividing the cost of an advertising campaign by the number of impressions, and expressing the result in terms of cost per 1,000 impressions. A floor CPM is the lowest price that an advertiser is willing to pay for an ad impression, and is typically set by the advertiser or the publisher. The floor CPM is used to ensure that an advertiser's ads are not shown at a price that is lower than their desired minimum, and can help to prevent undervaluation or fraud in the ad market. Floor CPMs are often used in conjunction with other pricing models, such as cost-per-click (CPC) or cost-per-action (CPA).