Black market Definition
The black market is the sector of economic activity in a jurisdiction involving illegal activities. Depending on the sense in which the term is used, this can primarily refer to illegally avoiding tax payments, to the profits of narcotic trafficking, or profits made from theft. It is so called because "black economy" or "black market" affairs are conducted outside the law, and so are necessarily conducted "in the dark", out of sight of the law.
Black markets are said to develop when the state places restrictions on the production or provision of goods and services that come into conflict with market demands. These markets prosper, then, when state restrictions are heavy, such as during prohibition or rationing. However, black markets are normally present in any given economy; where there are laws, someone will break them.