Blockchain is a digital ledger technology used to record and store transaction data in a secure, distributed, and immutable way. It is essentially a linked list of records, called blocks, that are secured using cryptography and maintained by a network of computers rather than a single entity. Blockchains are an essential component of cryptocurrency as they are used to record and store every single transaction that is made with the coins. Transactions are grouped into blocks and recorded chronologically, which allows users to trace their coins back to the point of origin and ensure that the transactions are secure and verifiable. In this way, blockchain technology is what enables cryptocurrencies like Bitcoin and Ethereum to exist.