Cost per thousand impressions of an online ad. When an ad is served to a user, it’s counted as an impression. If an ad network charges you $1,000 for delivering 1 million impressions, your CPM is $1. A CPM model can be a good strategy if your campaign goal is to raise awareness of your brand. If your campaign goal is to increase user interaction with your brand or prompt users to take a specific action such as signing up for a loyalty program, a cost-per-click (CPC) model may be a better choice.