Stable coins are more than those pegged with fiat.

Aside USDT, USD, DAI and others fiat begged stable coins, stable coins can be pegged with any other thing. Example is wBTC that is pegged with bitcoin price. Another example is PAXG and XAUt that is pegged with gold and so on. They are stable coins because the coin or asset they are pegged have almost the same price with them. As the asset go up, they go up and aas the asset come down, they come down. I mean in price.