DeFi infrastructure is the layer of foundational protocols and services — price oracles, stablecoins, bridges, and indexing services — that decentralised finance applications depend on but do not themselves implement. It sits beneath end-user-facing DeFi protocols such as lending markets and exchanges, supplying reliable price feeds and settlement assets like USDC that those protocols compose into their own functionality. Its reliability and decentralisation materially affect the security of everything built on top of it.