Smart contracts are self-executing contracts with terms directly written into code. They play a crucial role in blockchain development by automating and enforcing agreements without intermediaries. Smart contracts run on blockchain platforms like Ethereum and execute transactions or actions when predefined conditions are met. They enhance transparency, reduce costs, and eliminate the risk of manual errors. By providing a secure and immutable way to handle transactions, smart contracts are integral to decentralized applications (dApps) and various blockchain-based solutions.