Blockchain is a decentralized and secure digital ledger technology that records transactions across multiple computers. It ensures transparency, security, and immutability by using cryptographic techniques. Each block in the chain contains a set of transactions, and once added, it cannot be altered. This technology is widely used in cryptocurrencies like Bitcoin, but it also has applications in supply chain management, finance, healthcare, and more. Blockchain eliminates the need for intermediaries, making transactions faster and more efficient.