CPC - CPC stands for cost-per-click. It is the final amount you're charged for a click that user/visitor clicked on your ad.
CPA - CPA Stands for Cost-per-Aquisition. It is an online advertising pricing model where the advertiser pays for a specified acquisition - for example a sale, click, or form submit
CPM - This metric shows Cost per 1,000 impressions(the M is the Roman numeral abbreviation for 1,000). Most commonly used for buying media.
CTR - Click-through rate is the rate at which your PPC ads are clicked. This number is the percentage of people who view your ad (impressions) and then actually go on to click the ad (clicks). The formula for CTR looks like this: (Total Clicks on Ad) / (Total Impressions) = Click Through Rate.