A currency is a nation state legal tender, this idea was literally invented by governments. There are over 140+ currencies in the world today and each issued by their respective governments
Discussion
I believe that is the definition of Fiat Currency.
Currency is anything that people use to trade. Could be anything.
Stablecoins are a currency.
There is a distinction between money and currency. Is Gold a currency or money?
Money is anything that is ideally bearers property that people use to trade
Currency was first a derivative of money (Gold/silver/livestock etc) in early civilization