What is your understanding of DeFi?
DeFi is a contrast with Centralized Finance, where the entities are typically have the following properties: closed, proprietary, and trusted. The Nasdaq would be an example of centralized finance.
Uniswap illustrates the properties of decentralized finance: the technology is open source; the transaction are visible on the blockchain; participation is trust minimized, for example, liquidity provider can be anyone with a crypto wallet.
Based on these principles, the core primitives are largely swapping and lending; and lots of additional products built on top of these concepts.