EPC stands for 'Earnings per 100 Clicks'. It's a measure of how much one is making every 100 clicks on an ad.
For example, I received a total of $50 commission from 100 clicks on my banner ad. My EPC would be $50/100= $0.50. That is to say on average I made 50 cents from each person who clicked on the ad.
Again it's not another type of commission, just a gauge to see how well your ad is performing.
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