fiat money

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Legal tender, especially paper currency, authorized by a government but not based on or convertible into gold or silver.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun economics Money that is given legal value or made legal tender for money debts by government fiat.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun money that the government declares to be legal tender although it cannot be converted into standard specie