Money that serves as a medium exchange but does not have its own intrinsic value.
(Peter Dungan, Toronto PPG1002H and Mankiw, N. Gregory, Ronald Kneebone, Kenneth J. McKenzie and Nicholas Rowe. 2008. Principles of Macroeconomics, 4th Canadian ed. Toronto: Thomson Nelson.)
By definition, fiat money must be almost completely costless to produce. All developed modern economies use “fiat” money.