Would you enter into a contract with someone whom you’ve never met, and therefore don’t know and don’t trust? Would you become an investor in a small company in a foreign country? Would you agree to lend money to a stranger, like a farmer in Guatemala, a teacher in China, or to a cashier in the UK? Or would you set up a legally binding contract for a 1 EUR-purchase over the Internet, like buying a song from an artist? The answer in all of the above-mentioned cases is probably no, as the cost of setting up the necessary legal contract to secure your transaction is too high. We either don’t enter into such a contract at all or use trusted intermediaries to settle such contracts, paying them substantial settlement fees for their services.

A smart contract is a self-enforcing agreement embedded in computer code managed by a blockchain. The code contains a set of rules under which the parties of that smart contract agree to interact with each other. If and when the predefined rules are met, the agreement is automatically enforced. Smart contracts provide mechanisms for efficiently managing tokenized assets and access rights between two or more parties. One can think of it like a cryptographic box that unlocks value or access, if and when specific predefined conditions are met. The underlying values and access rights they manage are stored on a blockchain, which is a transparent, shared ledger, where they are protected from deletion, tampering, and revision. Smart contracts, therefore, provide a public and verifiable way to embed governance rules and business logic in a few lines of code, which can be audited and enforced by the majority consensus of a P2P network.

More detail: https://blockchainhub.net/smart-contracts/