Smart Contract
A program stored on a blockchain that executes automatically when its conditions are met.
A smart contract is a program stored on a blockchain that runs exactly as written when triggered — no intermediary needed. “If X happens, do Y”: release payment when goods are confirmed, swap token A for token B at the market rate, pay interest every block.
Ethereum popularized smart contracts in 2015, and they now power essentially all of DeFi, NFTs and blockchain gaming. Their strength — code that cannot be stopped or reversed — is also their weakness: a bug is permanent and publicly exploitable, which is why serious projects publish security audits before launch.