A blockchain is a type of digitally distributed database using an append-only list of data records ('blocks').
Blocks are organized in chronological order and are linked and secured using cryptography. Once recorded, a block cannot be altered retroactively without altering all subsequent blocks. Blockchains are typically used as a decentralized distributed ledger, recording all previously confirmed transactions.
Public blockchains are distinct from databases on centralized environments such as AWS in several key respects: blockchains have no central point of failure for technical or legal breaches, permissionless access to anyone with an internet connection, and reliance on incentive mechanisms rather than legal liability or corporate goodwill to maintain the integrity of the ledger.