Immutable Ledger

An immutable ledger is a record of transactions that, once written, cannot be quietly changed or deleted, only added to. Each new entry is linked to the ones before it, so tampering with an old record would break the chain and be obvious to everyone keeping a copy.

It is like a guest book written in permanent ink where every page is photographed by many witnesses: you cannot tear a page out unnoticed. An immutable ledger matters because it lets parties who do not fully trust each other share one history of events they can all rely on.