A blockchain is a type of distributed ledger technology that records transactions across multiple computers in such a way that the registered data cannot be altered retroactively. This structure is made up of blocks containing transaction data, which are linked together in a secure and verifiable manner. Each block includes a unique cryptographic hash of the previous block, creating a chain. Blockchain's decentralized nature enhances transparency, accountability, and security, making it applicable in various sectors such as finance, supply chain management, and digital identity verification.