Blockchain

A blockchain is a ledger, meaning a running record of transactions, that many computers store and update at the same time instead of one company keeping it. Transactions are grouped into batches called blocks, and each block is added in order and linked to the one before it. The network's rules make changing a past entry extremely difficult.

If someone sends you a unit of a cryptocurrency, no physical object moves. What changes is the shared record: the sender's balance falls and yours rises.

One common use is cryptocurrencies, digital assets whose ownership is tracked this way. The value can fall sharply and stay down, and losing the private keys, the secret codes that control a balance, can mean losing it all. Transfers usually cannot be reversed, and balances carry no FDIC insurance, which covers deposits at FDIC-insured US banks.