In web3, a contract often refers to a smart contract, which is a self-executing contract with the terms of the agreement directly written into code. These contracts run on blockchain technology, allowing for trustless transactions without the need for intermediaries. Smart contracts are immutable, meaning they cannot be changed once deployed, and are transparent, as they can be viewed and verified by all parties involved. They play a crucial role in facilitating decentralized applications (dApps), allowing developers to create a variety of services from games to financial instruments.