According to wikipedia A smart contract is a computer program or a transaction protocol that is intended to automatically execute, control or document legally relevant events and actions according to the terms of a contract or an agreement.
One easy example, When we use Starbucks, If our prepaid card's balance was lacking then It will charge the balance automatic.
Blockchain's Smart contract is that Smart Contract working in Blockchain.
It has two advantages.
First, there is no problem, even if they do not trust opponent.
Second, can reduce costs bacause, there is no moderator.
Taking advantage of the above advantages, People use Blockchain for employment contract system, and car rental.
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