SeatBid object
A SeatBid groups the bids a bidder makes on behalf of one buyer seat, such as an advertiser or agency account. A bid response carries these groups in BidResponse.seatbid, and each one holds one or more Bid objects.
How it is used
Seats are how exchanges apply buyer-level rules: the request's BidRequest.wseat and BidRequest.bseat lists, seat restrictions on deals in Deal.wseat, and seat-level reporting. A bidder acting for several buyers returns one SeatBid per seat, and a seat may bid on several impressions, or several times on the same impression.
The Bid response anatomy page covers it in more depth.
Fields
Where it sits
Contained in: BidResponse.
Contains: Bid.
All objects
The field reference index lists every OpenRTB 2.x object.