Blockchain

A blockchain is a shared, append-only ledger maintained across many computers, where records are grouped into blocks and each block cryptographically references the one before it. This chaining makes past entries expensive to alter, because changing one block would break every link after it. Networks use consensus rules to agree which blocks are valid, so no single party controls the record.

A common misconception is that a blockchain keeps data private or makes it “unhackable”; most blockchains are public and permanent rather than confidential. For a fuller walkthrough, see what a blockchain actually is.