What are secret nodes?

Could you please clarify what you mean by "secret nodes" in the context of cryptocurrency and finance? Are you referring to a specific type of network node that operates with a heightened level of privacy or anonymity? Or is it perhaps a concept related to decentralized finance (DeFi) where nodes might be involved in secret transactions or computations? It would be helpful to have a more precise definition or context in order to provide an accurate description.