The distributed ledger technology that underpins most cryptocurrencies is blockchain technology.
A blockchain stores records in blocks that are linked using cryptographic hashes. Copies of the ledger are maintained across a peer-to-peer network, and a consensus process determines which new transactions are accepted. This arrangement lets participants verify transactions without relying on one central database administrator.
The modern cryptocurrency use of blockchain was proposed by Satoshi Nakamoto in 2008 and implemented in Bitcoin in 2009. Its design addressed the double-spending problem: digital units could be transferred without requiring a central authority to keep the definitive account.
Blockchain is a type of distributed ledger, not a synonym for every distributed ledger. Alternatives such as Hashgraph use different data structures and consensus approaches, while Bitcoin and Ethereum are cryptocurrencies or blockchain platforms rather than the general technology itself. Blockchains can be public, private, permissioned, or permissionless.