An introduction to DeFi and how Upstream is making it more accessible with its blockchain-powered retail trading app — By Anastasia Samaras Decentralized Finance (DeFi) Decentralized Finance, or DeFi, falls deep within the crypto sector of fintech. It refers to digital assets, financial smart contracts, protocols, and applications (dApps) built on decentralized blockchains, most commonly Ethereum. DeFi is designed to be more transparent, accessible, and secure than the traditional financial system.