Tether USDT was designed to be pegged to the US dollar for stability, away from the uncertainties of the crypto market. Unlike a majority of cryptocurrencies, it does not have a finite token supply. Rather, the entity behind it issues new tokens when customers buy them by making deposits of USD and the other underpinning fiat currencies.
Therefore, theoretically at least, the tokens are only issued when there is demand, and for every USDT token in circulation, the company holds $1 in reserve. This keeps the price of USDT equivalent to its fiat equivalents at all times, theoretically.