Cost per One Thousand Impressions is a marketing term that refers to the price a thousand ad views on a single page. Its often abbreviated as CPM, which stands for Cost per M, referring to the Roman numeral for one thousand. CPM is the standard pricing method in online marketing. It is set by each publisher, according to a number of different factors, which means that the value of CPM can vary significantly from one publisher to another. One of the most important factors in determining the success of a CPM campaign is the click-through rate, that is, the ration between ad clicks and ad views.