Digital tokens recorded on a blockchain, a shared ledger no single company controls. Bitcoin and ether are the largest. A stablecoin is a token meant to hold a fixed value, usually one dollar; since a 2025 federal law, U.S. payment stablecoin issuers must back each token one-for-one with cash and short-term Treasuries and publish monthly reports. You hold crypto either in your own wallet (you control the keys) or at an exchange (they do).