Is USDT also Ethereum?

Could you please clarify for me if USDT is also considered to be a part of the Ethereum ecosystem? I've heard some discussions about cryptocurrencies and their association with different blockchains, and I'm a bit confused about the exact relationship between USDT and Ethereum. Is USDT issued or hosted on the Ethereum network? Does it share the same underlying technology as Ethereum? Or is it completely separate? I'd appreciate it if you could provide a concise explanation to help me understand this better. Thank you in advance for your assistance.