Blockchain is a decentralized, distributed ledger technology that is used to record and track transactions securely. It is a chain of blocks, each of which contains a record of multiple transactions. The blocks are linked together using cryptography, and are distributed across a network of computers, called nodes. This makes it difficult for any single person or entity to tamper with the ledger, as any changes to the ledger would have to be made on every node in the network. Blockchain technology is often used for applications that require a high level of security and transparency, such as financial transactions, supply chain management, and voting systems. It is also the underlying technology for cryptocurrencies such as Bitcoin.