CPM (Cost per Thousand Impression) based advertisements are a good way to earn income with your blog. CPM advertising pays you according to impressions of an advertisement. Abbreviated as CPM (the letter "M" in the abbreviation is the Roman numeral for one thousand). CPM is used by Internet marketers to price ad banners. Sites that sell advertising will guarantee an advertiser a certain number of impressions (number of times an ad banner is downloaded and presumably seen by visitors.), then set a rate based on that guarantee times the CPM rate.