USDT (Tether) is the world's largest stablecoin, designed to track the US dollar at a one to one ratio. Issued by Tether Limited and first launched in 2014, USDT is backed by reserves that include cash, cash equivalents and US Treasury bills. Because its value stays close to one dollar, traders use it to move in and out of volatile assets without leaving the crypto market, and many people use it to send dollars across borders quickly. USDT runs on several blockchains, including Tron, Ethereum and Solana. Stablecoins carry risks, including questions about reserves and regulation, so it helps to understand how they work before holding them.