Is Uniswap under Ethereum?

I've been hearing a lot about Uniswap recently, and I'm trying to wrap my head around how it fits into the crypto landscape. Could you clarify for me if Uniswap operates under the Ethereum blockchain? I'm curious to know if it's a decentralized exchange built on Ethereum's smart contract functionality, or if it's an independent platform with its own unique characteristics. Understanding this relationship would help me better grasp the intricacies of the crypto ecosystem.