singleton

 singleton  is in the context of the indieweb, or decentralized web in general, a shared (effectively centralized) data structure (like a blockchain ledger) or database (like the consequence of assuming a specific hashing algorithm) being used by (and thus a limitation of) an otherwise seemingly distributed system. More: https://www.scuttlebutt.nz/stories/design-challenge-avoid-centralization-and-singletons#avoiding-singletons.