A smart contract is on-chain code that automatically executes rules when transactions call it.
DeFi protocols, NFT mints, and DAOs are mostly smart contracts. Once deployed, code is hard to change without upgrade patterns.
In research workflows, Smart contract is usually interpreted with Solidity, DeFi, EVM, and Rug pull rather than as a standalone signal. Throughput, finality, and fee markets determine user experience and where activity migrates during congestion.