Metric object
A Metric reports one measured property of an impression, such as recent viewability or click-through rate, so a bidder can price it before bidding. The exchange sends them as an array in imp.metric, each with a type name, a value, and the vendor that measured it.
How it is used
Metrics appeared in OpenRTB 2.5. Exchanges decide which metric names they send and publish that list to buyers ahead of time, so the same idea can arrive under different names from different sellers. Bidders usually map each exchange's names onto their own model inputs and ignore names they do not recognize.
Fields
Where it sits
Contained in: Imp.
All objects
The field reference index lists every OpenRTB 2.x object.