The pricing model of advertising campaigns in which an advertiser pays per conversion (e.g. file download or form registration). CPA = total cost of campaign ÷ number of conversions.
This covers a range of other options depending on the goal of the ad, including cost per download (CPD) and cost per install (CPI).
One of the main advantages of the CPA model is that advertisers only pay for the results, essentially removing any false results found in other pricing models, such as fake views with the CPM model (see cost per mille).
eCPA means effective cost per acquisition and is used to show what the CPA would have been if the advertiser purchased conversions instead of impressions or clicks.