Cost per impression

Definition
Cost per impression (often abbreviated to CPI or CPM for Cost per thousand impressions, is a phrase often used in online advertising and marketing related to web traffic. It is used for measuring the worth and cost of a specific e-marketing campaign.

Overview
This technique is applied with web banners, text links, e-mail spam, and opt-in e-mail advertising, although opt-in e-mail advertising is more commonly charged on a cost per action (CPA) basis, although sometimes CPM is used.