"Black Book" is the nickname frequently used to refer to a list of people who are unwelcome in casinos.
The term can refer either to such a list officially maintained by a particular gaming control board or to the Griffin Book, whose information is shared among subscribing casinos.
[1] According to technologist Jeff Jonas, "Casinos face legal and financial risk if they let the wrong people play.
"[2] In the case of gaming control boards, people listed are generally suspected of having, or known to have, ties to organized crime.
Casinos are obliged by regulations to exclude all such people from entry and can be subject to sanctions for failure to do so.