A smart contract is a piece of software that executes automatically when predetermined conditions are met. It requires no human to process it, no institution to authorize it, and no counterparty to trust it. In the context of decentralized finance, this is not a minor technical detail — it is the entire architecture. Defi exists because smart contracts make it possible to replicate the functions of financial intermediaries in code.

Decentralized finance — defi — is not a single product or platform. It is a collection of financial goods and services that operate through automated software programs called smart contracts, running on public blockchains, accessible in principle to anyone with the requisite technical knowledge and some quantity of cryptocurrency. The Congressional Research Service, in an April 2026 overview of the sector, defines it as a system characterized by “highly automated financial networks that have no single point of failure, do not rely on a single source of information, and are not governed by a central authority.”