What is the difference between Uniswap and Ethereum?

Could you please elaborate on the distinction between Uniswap and Ethereum? As I understand, they are both intricately linked within the cryptocurrency sphere, yet I'm still hazy on their specific roles and differences. Uniswap, I believe, is a decentralized exchange, facilitating peer-to-peer trading of various tokens. But how does it differ from Ethereum, which I know is a blockchain platform enabling smart contracts and distributed applications? Is Uniswap built on Ethereum? If so, how does this relationship impact their functionalities and use cases? I'm eager to gain a deeper understanding of these two entities and how they interact within the broader cryptocurrency ecosystem.