The Full form of CPM is Cost per Mile. CPM is also called cost per thousand as in Latin terms, the word mile means one thousand. The word refers with context to the marketing term that refers to the price of one thousand advertisement impressions on a web page. For example, if a publisher of a website charges Rs. 200 CPM, it means a person have to pay Rs. 200 for every 1,000 impressions of its ad. So, it is considered as a widely used method for web ads pricing.
The success of a CPM (Cost per Mile) campaign is measured by its CTR (click-through rate), which reflects the percentage of people who have seen your ad and clicked on it. For example, an advertisement that got 10 clicks for every 200 impressions has a 5% CTR. However, the success of a web advertisement cannot be solely measured by Click-Through Rate as an ad that is not clicked by a user but viewed can also have an impact.