Tether is a stable coin, whoes value is pegged to that of US dollar. 1 USD= 1USDT,The value of USDT can sometime fluctuate by a few decimal points due to demand but its price is never that far away from $1 mark. That's why when there is much fluctuation in the crypto currencies, Investors usually prefer to go for stable coins.
See below .
https://www.offshorecorptalk.com/threads/why-is-tether-considered-a-stable-coin.28000/post-119084