DeFi stands for decentralized finance, and includes financial services run by smart contracts on blockchains, such as lending, borrowing, trading, and yield, without traditional intermediaries taking custody or granting permission. It is typically built on public, permissionless networks (anyone with a wallet can participate), though some setups add permissions or compliance layers.

Decentralization in DeFi is a spectrum: execution may be fully on-chain while other parts (governance, front-ends, oracles) vary. The core idea is programmable, self-custodied finance with open access.