The Collaborative International Dictionary of English v.0.48:

black market \black market\ n.
   1. the illicit buying and selling of goods, in violation of
      price controls, rationing, tax laws, prohibition of sale,
      etc.
      [PJC]

   2. a place where such illegal commerce is conducted, or the
      entire system of such illicit commerce considered as a
      whole; as, the black market accounts for twenty percent of
      the Ukrainian economy.
      [PJC]

WordNet (r) 3.0 (2006):

black market
    n 1: people who engage in illicit trade
    2: an illegal market in which goods or currencies are bought and
       sold in violation of rationing or controls
    v 1: deal in illegally, such as arms or liquor [syn: run,
         black market]