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The phrase and concept of smart contracts was developed by Nick Szabo as far back as 1994, with the goal of bringing what he calls the "highly evolved" practices of contract law and practice to the design of electronic commerce protocols between strangers on the Internet. Nick is a computer scientist known for his research in digital contracts and digital currency. Although Szabo has repeatedly denied it, people have speculated that he is the one behind Satoshi Nakamoto, the designer of Bitcoins.
In 1996, as part of a startup doing bond trading on the net, Ian Grigg created a method to bring a classical 'paper' contract into touch with a digital accounting system such as cryptocurrencies. The form, which became known as the Ricardian Contract, was readily usable for anything that you could put into a written contract, beyond its original notion of bonds.
In short: write a standard contract such as a bond. Insert some machine-readable tags that would include parties, amounts, dates, etc that the program also needed to display. Then sign the document using a cleartext digital signature, one that preserves the essence as a human-readable contract. OpenPGP works well for that. This document can be seen on the left of this bow-tie diagram.
Definition
A smart contract is a collection of code (its functions) and data (its state) that resides at a specific address on the Ethereum blockchain. Contract accounts are able to pass messages between themselves as well as doing practically Turing complete computation. They are little programs that execute “if this happens then do that”, run and verified by many computers to ensure trustworthiness.
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