A blockchain is a decentralized, cryptographically linked database that stores transactions in blocks and appends them in an immutable, tamper-evident chain.
Each new block contains a hash reference to the previous block, creating a chronological chain that is practically impossible to alter retroactively without also changing every subsequent block.
Instead of a central authority like a bank, a network of many computers (nodes) jointly maintains the ledger. New entries must be confirmed by a majority of the network through a consensus mechanism such as Proof of Work or Proof of Stake before they are permanently recorded.
Blockchains are the technical foundation of cryptocurrencies like Bitcoin, but are increasingly also used for smart contracts, supply-chain tracking and digital identity systems.
