Unlike a commodity currency, fiat money is not backed by any physical asset such as gold or silver. Instead, it relies on the faith people have in the currency and the government behind it. The U.S. dollar is a fiat currency and is considered the least risky currency of all the other fiat currencies. The U.S. dollar has become a global safe haven because of the U.S. government’s stability. It is backed by the "full faith and credit" of the U.S. government.
A fiat currency provides a country’s central bank with more control over the money supply — credit supply, liquidity, interest rates, and money velocity. Because central banks can print money, unless there are checks and balances, the situation can get out of control, leading to hyperinflation, as was the case in Zimbabwe and the Weimar Republic of Germany.