Definition of 'Blind Brokering'
When brokerage firms ensure anonymity to both the buyer and the seller in a transaction. In the ordinary course of securities trading, most brokerage transactions are "blind". Exceptions occur for broker/dealers or others acting as both broker and principal on a given trade
Investopedia explains 'Blind Brokering'
Disclosure to either the buying or selling party of the identity of the other is not the norm in public securities trading, except in some cases of privately arranged transactions.
The only exception to this is when the broker is a principal and selling securities from its own inventory to a customer of the firm. In this case, disclosure is required due to a possible conflict of interest.