What is Lido stETH?

I'm curious, could you elaborate on what exactly Lido stETH is? As a professional in the field of cryptocurrency and finance, I've come across various tokens and protocols, but this one piques my interest. Is it a derivative of ETH? How does it fit into the broader ecosystem of Ethereum? And what kind of utility does it offer to investors and users alike? I'm eager to understand its role in the crypto finance landscape.