What chain is Polkadot on?

Excuse me, but could you clarify something for me? I'm curious about the underlying blockchain technology that Polkadot operates on. Specifically, what chain does Polkadot utilize, and how does this chain contribute to its unique functionality and features, such as its interoperability and scalability? I'm looking to gain a deeper understanding of the technical underpinnings of this innovative cryptocurrency and blockchain platform.