Background

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:

1. the illegal economy
2. the unreported economy
3. the unrecorded economy
4. the informal economy

The "illegal economy" consists of the income produced by those economic activities pursued in violation of legal statutes defining the scope of legitimate forms of commerce. Illegal economy participants engage in the production and distribution of prohibited goods and services, such as drug trafficking, arms trafficking, and prostitution.

The "unreported economy" consists of those economic activities that circumvent or evade the institutionally established fiscal rules as codified in the tax code. A summary measure of the unreported economy is the amount of income that should be reported to the tax authority but is not so reported. A complementary measure of the unreported economy is the "tax gap", namely the difference between the amount of tax revenues due the fiscal authority and the amount of tax revenue actually collected. In the U.S. unreported income is estimated to be $2 trillion resulting in a "tax gap" of $450–$600 billion.

The "unrecorded economy" consists of those economic activities that circumvent the institutional rules that define the reporting requirements of government statistical agencies. A summary measure of the unrecorded economy is the amount of unrecorded income, namely the amount of income that should (under existing rules and conventions) be recorded in national accounting systems (e.g. National Income and Product Accounts) but is not. Unrecorded income is a particular problem in transition countries that switched from a socialist accounting system to UN standard national accounting. New methods have been proposed for estimating the size of the unrecorded (non-observed) economy. But there is still little consensus concerning the size of the unreported economies of transition countries.

The "informal economy" comprises those economic activities that circumvent the costs and are excluded from the benefits and rights incorporated in the laws and administrative rules covering property relationships, commercial licensing, labor contracts, torts, financial credit and social security systems. A summary measure of the informal economy is the income generated by economic agents that operate informally.page needed The informal sector is defined as the part of an economy that is not taxed, monitored by any form of government, or included in any gross national product (GNP), unlike the formal economy. In developed countries the informal sector is characterized by unreported employment. This is hidden from the state for tax, social security or labour law purposes but is legal in all other aspects. On the other hand, the term black market can be used in reference to a specific part of the economy in which contraband is traded.