eCPM (effective CPM)

eCPM is what an ad placement earned or cost per thousand impressions, whatever way it was actually priced.

It converts CPC, CPA and flat-fee deals into a CPM so they can be compared: total cost (or revenue) divided by impressions, times 1,000.

Publishers use it to compare demand sources; buyers can use it to see what a flat sponsorship really costs per thousand people reached.