Is USDT the same as ETH?

Could you clarify for me the difference between USDT and ETH? Are they interchangeable, or do they serve distinct functions within the cryptocurrency landscape? I've heard that both are popular tokens, but I'm not quite sure how they differ from each other. Is USDT simply a stablecoin pegged to the US dollar, while ETH is the native token of the Ethereum blockchain? Could you elaborate on their unique characteristics and uses? I'm particularly interested in understanding how investors might utilize these two tokens differently in their portfolios.