Is USDT ERC20 or TRC20?

Could you please clarify for me if USDT is ERC20 or TRC20? I've been hearing about both standards in the context of cryptocurrencies, but I'm still a bit confused about the differences and which one USDT falls under. ERC20 seems to be a widely used standard on the Ethereum blockchain, while TRC20 is associated with the Tron network. Given that USDT is a stablecoin designed to maintain a 1:1 peg with the US dollar, I'm curious to know which of these two standards it adheres to. Could you enlighten me on this matter? Your explanation would be greatly appreciated.