A blockchain is a distributed database that maintains a continuously growing list of records, called blocks, secured from tampering and revision. Each block contains a timestamp and a link to a previous block.
By design, blockchains are inherently resistant to modification of the data - once recorded, the data in a block cannot be altered retroactively.
Through the use of a peer-to-peer network and a distributed timestamping server, a blockchain database is managed autonomously.
Blockchains are "an open, distributed ledger that can record transactions between two parties efficiently and in a verifiable and permanent way.