Blockchains are digital ledgers that are used to record and store transaction information. They are made up of blocks, which are digital records of transactions, secured by cryptography. Each block contains a cryptographic hash, a timestamp, and transaction data. When a new transaction is made, the data is added to the block, and the block is added to the blockchain. Each block is connected to the previous block, forming a chain of blocks, hence the term blockchain. As each block is added to the chain, it becomes more secure, making it virtually impossible for anyone to alter or delete the data. The blockchain is maintained by a network of computers, called nodes, which run software that verifies and records transactions.