A type of distributed ledger, written on open source software. It is a growing database of time-stamped transactions that cannot be altered. Each new transaction is verified by a network of computers and added as a “block” to the chain.
Each block is ‘chained’ to the next block using a cryptographic signature. Ethereum is a public blockchain, open to the world; its digital ledger is distributed, or synced, between many nodes; these nodes arrive at consensus regarding whether a transaction is valid before encrypting a number of transactions into a block.