Media term describing the cost of 1,000 impressions. Online advertising can be purchased on the basis of what it costs to show the ad to one thousand viewers (CPM). It is used in marketing as a benchmark to calculate the relative cost of an advertising campaign or an ad message in a given medium. Rather than an absolute cost, CPM estimates the cost per 1,000 views of the ad. For example, a website that charges $1,500 per ad and reports 100,000 visits has a CPM of $15 ($1,500 divided by 100).