An exchange (venue) in which offers to trade are not disclosed to the public. Orders can be invisibly transmitted (and hence are called dark orders) in many ways including hidden orders and iceberg orders carried in limit order books, and invisible positions in agency orders posted by brokers, as well as undisclosed dealer liquidity, latent orders by passive, buy-side investors, and orders on the blotters of buy-side and sell-side properietary desks, etc.
It is also called a dark market.
