CPM stands for "Cost Per Mille", where "mille" is the Latin term for a thousand. In the context of advertising, CPM represents the cost per thousand impressions, meaning the amount an advertiser pays for every thousand views of their ad.
For example, if an advertiser pays $10 for a CPM, it means they are paying $10 for every 1,000 impressions of their ad.
It's a metric commonly used in digital advertising to gauge the cost of an advertising campaign based on visibility and reach, rather than direct user interaction (like clicks).