Smart contract

A smart contract is a program stored on a blockchain that runs exactly as written when someone sends it a transaction. Once deployed, its code and state are public, and nobody can stop it unless the contract itself contains admin controls. Ethereum popularised smart contracts. Solana, Avalanche, BNB Chain, Cardano and many other networks support them too.

Smart contracts power tokens, decentralised exchanges, lending markets, NFTs and stablecoins. They let strangers transact under shared rules without trusting an intermediary.

They are not legal contracts, and "code is law" cuts both ways: a bug can be exploited and funds drained with no way to reverse it. Hundreds of millions of dollars have been lost in contract hacks. Audits reduce but do not eliminate risk. Also check whether a contract can be upgraded or paused by an admin key.