Blockchain
termcryptographyprogramming
An append-only ledger of batched transactions in which each block carries the cryptographic hash of the one before it, so altering any past record changes every hash after it. Combined with a consensus rule that decides which chain counts, it lets mutually distrustful parties agree on an order of events with no central authority.
The data structure is old - hash chains and Merkle trees, plus Haber and Stornetta's 1991 timestamping work - and the 2008 Bitcoin paper's real contribution was the incentive layer that makes rewriting history expensive. What blockchains actually guarantee is narrow and worth stating precisely: ordering and tamper-evidence, not truth. Garbage written correctly to a chain is permanent garbage, and most problems reached for by the word are solved better by a database with an audit log.
Also known as: distributed ledger, chain of blocks, proof of work