What does interoperability mean (wrt online ad exchanges)?

What does interoperability mean?

In the simplest terms it means:

* Supply can originate in one exchange but be made available for sale to buyers from other exchanges.

* Demand can originate in one exchange but flow into other exchanges. For instance, an ad buyer can express its targeting rules, bids and budget on one exchange but also be connected to and able to buy supply originating from other exchanges.

More broadly, this means supply and demand can interact — regardless of the primary exchange their owners (publishers in the case of supply and ad buyers, including networks, agencies and advertisers in the case of demand) are participating in.

via Google And Yahoo To Work Together (YHOO, GOOG).