“If you pay your cleaner or builder in cash, or for some reason neglect to tell the taxman that you were paid for a service rendered, you participate in the black or underground economy. Such transactions do not normally show up in the figures for GDP, so the black economy may mean that a country is much richer than the official data suggest. In the United States and the UK, the black economy adds an estimated 5-10% to GDP; in Italy, it may add 30%. As for Russia, in the late 1990s estimates of the black economy ranged as high as 50% of GDP” (The Economist).
Black economy. (n.d.). In Economics A-Z: Economic terms, topics and jargon. Retrieved October 7, 2009, from http://www.economist.com/research/Economics/alphabetic.cfm?term=blackeconomy#blackeconomy