A smart contract (self-executing contract, blockchain contract) is an agreement between parties that is enforced by a program encoded onto a blockchain which executes code exactly as originally written.
There is rapid development ongoing in the research and creation of smart contract languages used by the blockchain community. Ethereum uses a variety of smart contract languages including called Solidity. Solidity is a high-level language whose creation was influenced by JavaScriptJavaScript as well as python and C++. The Solidity language was created by members of the Ethereum foundation including Gavin Wood, Christian Reitwiessner, and others. Michelson is a language developed to write smart contracts on the Tezos blockchain. The smart contract platform being developed for the Rchain blockchain is called Rholang. Lisk smart contracts are written in Javascript. The Cardano blockchain defines smart contracts using a language called Plutus, which has syntax similar to Haskell. Chain has released a language called Ivy for writing high level code which compiles to Bitcoin Script code.