A blockchain is a distributed ledger with growing lists of records (blocks) that are securely linked together via cryptographic hashes. Each block contains a hash of the previous block, a timestamp, and transaction data. The timestamp proves that the transaction data existed when the block was created. Since each block contains information about the previous block, they effectively form a chain, with each block linking to the ones before it. Consequently, blockchain transactions are irreversible such that the data in any given block cannot be altered retroactively without altering all subsequent blocks.

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By Simplilearn

By 3Blue1Brown

By WIRED