A smart contract is a blockchain technology which maintaining specific rules depending on the parties for those agree with same rules to interact with each other. It is tamper resistant, self-executing and self-verifying. It can convert legal issues into automated methods. It is granted, highly secured and cost effective. It can work without or less involvement of intermediaries.
Smart contract record information, circumstance, relations, balances and required data to implement logic for real world agreement. A smart contract can use another smart contract which is satisfying different agreement to serve any new purpose of the 1st smart contract.
[Source: https://blockchainhub.net/smart-contracts/ ]