The recently coined financial term 'dark pool' seems to be ubiquitous. I came across it for the first time this weekend in two separate articles in The Financial Times, and it's probably in more articles that I skipped over - I buy the newspaper for the cryptic and general knowledge crossword mainly. I guess it's a recent term as it usually has quotation marks around it, or is prefaced by 'so-called', but despite that, googling the expression came up with over ten million hits.
The FT kindly gave a definition (full article here):
"... the emergence of "dark pools" of liquidity - a relatively new venue for the buying and selling of shares. Pre-trade prices - the price at which shares are offered for sale - are not visible to anyone, even the participants in them, and the price at which shares change hands is only revealed after the trade is done".
The fact that the expression contains the word 'dark' makes it sound fairly ominous. A quick search for the term online shows that words and expressions which often appear in the same sentence as the term 'dark pool' include opaque, anonymous trading venue, criticism, suspicion, need for regulation and alarm.