Smart Contract
In plain English
A program stored on a blockchain that runs exactly as written when its conditions are met — no company or middleman needed to enforce it.
What is a smart contract?
A smart contract is code deployed to a blockchain that executes automatically when specific conditions are met. The name is slightly misleading: it is not a legal document and it is not especially "smart". It is a program whose rules everyone can read and whose execution nobody can quietly change.
How it differs from ordinary software
Normal software runs on a server that its owner controls — they can edit it, pause it or shut it down. A smart contract runs on thousands of independent nodes, all of which must reach the same result. Once deployed, its code typically cannot be altered. That immutability is the point: users can verify the rules before trusting the contract with money.
What they are used for
Smart contracts underpin most of what happens on Ethereum and similar chains. Decentralised exchanges use them to swap tokens without an intermediary holding funds. Lending protocols use them to accept collateral and release loans automatically. Tokens themselves are smart contracts — an ERC-20 token is simply a contract tracking who owns what.
The risks
Because the code is final and controls real money, bugs are expensive and permanent. If a contract contains a flaw, an attacker can exploit it and there is usually no way to reverse the result. Hundreds of millions of dollars have been lost this way.
This is why audits matter, and why serious projects publish their code and have it reviewed by independent security firms. An audit reduces risk but never eliminates it — audited contracts have been drained too. Treat any contract holding your funds as software that can fail.