The rate at which the advertiser is charged for a placement, as entered in the placement properties. A placement's cost depends on the rate and the cost structure. You must book at least one unit per placement and include a cost structure in order to report on its placement rate.
For placements with a flat rate cost structure, the placement rate is the sum of costs for all flights. For CPM/vCPM - Active View/CPC/CPA cost structures, the placement rate is calculated as follows:
Placement rate = Sum of costs for all flights / (Sum of units for all flights / 1000)