“Dark trading” has a subterranean connotation, as if it were done by slithering snakes in the river Styx. In actuality, the term refers to trading in stocks that is done on computers that are less public than the exchanges. That is to say, the bid-and-ask quotations on a given computer network are known only to participants on it, and not to the traders on the public exchanges. Ethically, the public-private dichotomy is relevant. I submit that it reflects a wider trend in American society.
The full essay is at “Dark Trading”