Pulled this of of AI. It's a good, succint, clear definition of fiat currencies that includes technical facts that are often left out of short definitions.

I use duck.ai :

A fiat currency is a type of money that is established by government regulation or law. The term "fiat" comes from the Latin word for "let it be done" or "it shall be," reflecting the fact that fiat money is established by government decree. Unlike commodity-based currencies, fiat money is not backed by a physical commodity such as gold or silver. Instead, its value is derived from the trust and confidence that people have in the government and the economy that issues it.

Key characteristics of fiat currency include:

- Government Issuance: Fiat currencies are issued and regulated by central banks or governments.
- Legal Tender: They are accepted as a medium of exchange within the country that issues them.
- No Intrinsic Value: Unlike commodity-based currencies, fiat money does not have intrinsic value. Its value is based on supply and demand, as well as the stability and credibility of the issuing government.
- Flexibility: Governments can control the money supply, which can be used to influence economic conditions such as inflation and interest rates.

Examples of fiat currencies include the U.S. Dollar, the Euro, the Japanese Yen, and the British Pound. These currencies are widely accepted and used for transactions within their respective countries and internationally.