CPM is the the price (cost) per 1,000 impressions on a given media channel (digital, video/TV, OOH, or otherwise). It’s the most common unit of price-based measurement in advertising, and the most universal as well. Radio, television, newspaper, magazine, out-of-home advertising, and online advertising can be purchased on the basis of showing the ad to one thousand viewers.
Here’s a calculator to get the CPM from the intended or quoted cost, and the impressions anticipated. Enjoy!