Cost Per Mille (CPM) is a pricing model. It's is the advertising cost per thousand impressions viewed.
It's derived from the Latin word mille which means one thousand.
It’s the value of an individual ad impression, especially from the advertiser's perspective.
Based on how many impressions a single ad gets.
Direct sales are almost always priced in fixed CPM rates, where the inventory is sold in bulk and all impressions are essentially priced the same (e.g., 10 CPM, or 10 per thousand ad views).
Cost per thousand impression campaigns produce:
It dominates the content sites and is generally used with large, brand-oriented banner ads.
CPM works well for advertisers who are interested in raising the brand awareness
It can track:
CPM works well for publishers with a large audience and a growing number of monthly pageviews.
Facebook: Our COO Owen Van Natta told me to get 30 cent CPM guarantee for that space, substantially more than what Google gave MySpace.
Contextual ads such as Google AdSense and Media.net can produce the equivalent of 1-5 CPMs per ad unit based on the click-through rate.
https://convertkit.com/blog-advertising-networks/