Blockchain is a distributed digital ledger that records transactions in a verifiable and permanent way using cryptography. It was originally developed for the cryptocurrency Bitcoin but has expanded to other applications. The blockchain is composed of blocks that contain validated transactions. Each new block is cryptographically linked to the previous block, creating an immutable chain. Blockchain provides security, transparency and efficiency through decentralization and consensus mechanisms like proof-of-work. It has the potential to transform industries like finance, healthcare and logistics by reducing costs and intermediaries while increasing trust.