Because tax evasion or participation in a black market activity is illegal, participants will attempt to hide their behavior from the government or regulatory authority. Cash usage is the preferred medium of exchange in illegal transactions since cash usage does not leave a footprint. Common motives for operating in black markets are to trade contraband, avoid taxes and regulations, or skirt price controls or rationing. Typically the totality of such activity is referred to with the definite article as a complement to the official economies, by market for such goods and services, e.g. "the black market in bush meat".
The black market is distinct from the grey market, in which commodities are distributed through channels that, while legal, are unofficial, unauthorized, or unintended by the original manufacturer, and the white market.
Black money is the proceeds of an illegal transaction, on which income and other taxes have not been paid, and which can only be legitimised by some form of money laundering. Because of the clandestine nature of the black economy it is not possible to determine its size and scope.
The literature on the black market has not established a common terminology and has instead offered many synonyms including: subterranean; hidden; grey; shadow; informal; clandestine; illegal; unobserved; unreported; unrecorded; second; parallel and black.
There is no single underground economy; there are many. These underground economies are omnipresent, existing in market oriented as well as in centrally planned nations, be they developed or developing. Those engaged in underground activities circumvent, escape or are excluded from the institutional system of rules, rights, regulations and enforcement penalties that govern formal agents engaged in production and exchange. Different types of underground activities are distinguished according to the particular institutional rules that they violate. Four major underground economies can be identified: