Overview#Indy Steward are nodes of the Hyperledger Indy network that have permissions to participate in the validation process.
Hyperledger Indy is designed to be a global public network, an instance will have many available nodes located around the world - more nodes available than can be effectively used in the validation process. The validation process needs enough Indy Stewards to be robust in the face of faults, but not too many as to degrade the performance in reaching consensus.
Hyperledger Indy's solution is to have an optimal subset of Indy Steward perform Validation - actively participating in the Plenum Consensus Algorithm, and the rest as Observer nodes, tracking the growing Blockchain, serving reads (thus offloading that work from the Validators) and ready to called on to be Validators should they be required.
The image below from Sovrin (covered in the next section) shows the division of Validator nodes (those currently participating in writing to the Ledger) and the Observer nodes (read-only nodes, but ready to become Verifiers if needed).