Is USDT built on ETH?

Excuse me, I'm a bit confused about the relationship between USDT and ETH. Could you please clarify if USDT is built on the Ethereum blockchain? I understand that USDT is a stablecoin pegged to the US dollar, but I'm not sure about its underlying technology. Is it based on the ERC-20 token standard? If so, does it mean that USDT transactions are processed and settled on the Ethereum network? Also, how does this relationship affect the performance and scalability of USDT? Thank you for your help.