cost per thousand
Abbreviated as CPM (the letter "M" in the abbreviation is the Roman numeral for one thousand). CPM is used by Internet marketers to price ad banners. Sites that sell advertising will guarantee an advertiser a certain number of impressions (number of times an ad banner is downloaded and presumably seen by visitors.), then set a rate based on that guarantee times the CPM rate. A Web site that has a CPM rate of $25 and guarantees advertisers 600,000 impressions will charge $15,000 ($25 x 600) for those advertisers' ad banner.
See "How Affiliate Marketing Works" in the "Did You Know..." section of Webopedia.
Also see Refer-It.com, a directory of referral & affiliate programs for e-commerce, featuring information on over 6,500 affiliate programs.