Publisher object
The Publisher object identifies the seller of the inventory: the entity that supplies the impression to the exchange and is paid for it. It appears at site.publisher, app.publisher, and dooh.publisher. Since OpenRTB 2.6 its ID is meant to match a seller_id in the exchange's sellers.json file.
How it is used
Up to 2.5 the spec described this object as the publisher of the media, usually also the seller. OpenRTB 2.6 redefined it around payment, so an ad network or intermediary exchange appears here when it is the party the exchange pays. Buyers join Publisher.id to the exchange's sellers.json and to the exchange's own node in Source.schain to see who they are paying.
Fields
Where it sits
All objects
The field reference index lists every OpenRTB 2.x object.