Blockchains are the critical infrastructure underlying cryptocurrencies. The common feature of these distributed ledgers is the sequential updating of a cryptographically secure, verifiable transaction record among a network of peers all operating under a certain set of rules enforced through the software itself. This record is owned and operated in common by anyone anywhere.
While research in shared ledger technology goes back decades, the arrival of the Bitcoin blockchain introduced the first distributed ledger technology that was thoroughly decentralized and resistant to censorship, seizure and collusion.
Blockchain technology, in its various manifestations including the Ethereum blockchain and others, is ultimately a global consensus system — i.e., it allows people to coordinate and cooperate around a neutral source of information without trusting each other or a central administrator. The use cases are wide-ranging, from finance and energy trading to supply chain management.