Blockchain technology was described in 1991 by the research scientist STUART HABER and W. SCOTT STORNETTA. They develop a system using the concept of a cryptographically secured chain of blocks to store the time-stamped documents. Further, In 2008, SATOSHI NAKAMOTO conceptualized the theory of distributed blockchain. He improves a design in a unique way to add blocks to the initial chain without requiring them to be signed by trusted parties.

The word Block and Chain were used separately in Satoshi Nakamoto original’s paper but were eventually popularized as a single word, The BLOCKCHAIN, by 2016. Blockchain is a system of recording information in a way that makes it difficult or impossible to change, hack or cheat the system. A blockchain is essentially a digital ledger or transaction that is duplicated and distributed across the entire network of computer systems on the blockchain.

Each block in the chain contains a number of transactions, and every time a new transaction occurs on the blockchain, a record of that transaction is added to every participant's ledger. Blockchain is a constantly growing ledger that keeps a permanent record of all the transactions that have taken place in a secure, chronological, and immutable way.

1. Ledger: It is a file that is constantly growing.

2. Permanent: It means once the transaction goes inside a blockchain, you can put up it permanently in the ledger.

3. Secure: Blockchain places information in a secure way. It uses very advanced cryptography to make sure that the information is locked inside the blockchain.

4. Chronological: Chronological means every transaction happens after the previous one.

5. Immutable: It means as you build all the transactions onto the blockchain, the ledger can never be changed.

The term Smart Contract was first used by Nick Szabo in 1997 long before Bitcoin was created. He is a computer scientist, law scholar, and cryptographer but in simple terms: he wanted to use a distributed ledger (A record-keeping system, ledger maintains participant's identities anonymously.) now, a smart contract is just like contracts in the real world but the only difference is that they are entirely digital.

In fact, a smart contract is actually a tiny program that is stored inside a blockchain with the smart contract we can build a similar system that doesn’t require a third party. In smart contracts, there is no use of third parties because it is a decentralized procedure. In simple terms, we can say that "Smart Contracts" are a piece of code written in some specific language like Solidity or Vype and are deployed on blockchain to give raise to trustlessness or unbreakable promises and many more.

In normal contracts, if two parties want to contract but in between theirs some authority or we can say centralized procedure or third-party contract will be executed and it takes a lot of time but in smart contracts, there is no use of third-party because it is decentralized procedure directly contract with each other.