This refers to any kind of information barrier erected between different divisions of a financial institution or any other conglomerate, to prevent the unethical use of business information. A bank division that employs brokers to advise customers on what stocks to buy, for instance, may be barred from communicating with another division of the same bank that offers investment banking services to publicly listed companies. This wall is generally erected to prevent charges of conflict of interest. In some cases, banks may decide to completely spin-off their various business divisions into separate legal entities to prevent any malpractice.
