CPM stands for “cost per thousand impressions” and can be thought of as a measurement of advertising effectiveness based on the number of people who viewed the ad.
In many contexts, ads are considered more valuable when they have higher rates of exposure, including in high-traffic locations. The CPM value is calculated by taking the amount that was spent to display an advertisement (purchase price), and dividing it by how many impressions were made (viewings). Standardized CPM values are typically rated in dollars per 1,000 views.