A blockchain is a decentralized, distributed digital ledger that records the history of transactions across a peer-to-peer network. It is made up of blocks that store data in a secure and immutable way. Each block contains a cryptographic hash of the previous block, a timestamp, and transaction data. For example, the Bitcoin blockchain is a public ledger that records all Bitcoin transactions. It is maintained by a network of computers that must come to a consensus on the order of transactions.