What does Cost Per Impression (CPI or CPM) mean in SEO?

This is an option for advertisers offered by many websites as well as search engines such as Google, Yahoo and Bing.

Advertisers pay every time their advertisement is shown but (usually) pay nothing when a user clicks on it.

This type of advertisement is popular with companies who want brand awareness rather than for an internet user to click and visit their website. Such organisations might include Coca Cola or Dell Computers.

CPI stands for Cost Per Impression while CPM stands for Cost Per Thousand Impressions. The second term exists because cost per impression can often be so low it is difficult to state in financial terms while Cost Per Thousand can start at a few dollars or pounds.

Pay Per Impression should not be confused with Pay Per Click (PPC) advertising.