A fiat currency is one declared by a government, but there are many private currencies out there. For example, the Chiemgauer. https://en.wikipedia.org/wiki/C

A fiat currency is one declared by a government, but there are many private currencies out there. For example, the Chiemgauer. https://en.wikipedia.org/wiki/Chiemgauer https://en.wikipedia.org/wiki/Chiemgauer In most cases, using a different medium of exchange is legal. For example, a merchant can accept Euros if they choose.