SupplyChain object
SupplyChain records the path a bid request took from the inventory owner to the current sender: an ordered list of nodes, one per system that sold or resold it, and a flag for whether that list is complete. In OpenRTB 2.6 it lives at source.schain.
How it is used
The object was first published as a standalone IAB Tech Lab specification and carried in extensions (source.ext.schain in 2.5 integrations) until OpenRTB 2.6 made it part of the core model. Buyers check each node against sellers.json and ads.txt and use the result for supply path optimization and fraud filtering. Every system that passes the request on appends its own node, so the chain grows by one at each hop.
The Supply chain (schain) page covers it in more depth.
Fields
Where it sits
Contained in: Source.
Contains: SupplyChainNode.
All objects
The field reference index lists every OpenRTB 2.x object.