Fiat money is currency that a government has declared to be legal tender, but is not backed by a physical commodity. The value of fiat money is derived from the relationship between supply and demand rather than the value of the material that the money is made of. Historically, most currencies were based on physical commodities such as gold or silver, but fiat money is based solely on faith.
Greenback” 5 dollar (United States Note) Issued in 1862. The first use of fiat money (called Greenbacks) in the United States was in 1862, it was used as a tool to pay for the enormous cost of the Civil War. Greenbacks were a debt of the U.S. government, redeemable in gold at a future unspecified date. They were circulated along with Gold certificates, backed by the government’s promise to pay in gold.