Definition - What does Broker's Broker mean?
Broker's broker is a municipal bond dealer who specializes in executing orders for other dealers who are not active in the municipal bond market.
Testopedia explains Broker's Broker
Unlike most equity securities many municipal bonds are not actively traded and can be difficult to purchase or sell. In these cases a broker dealer who is not active in the municipal bond market may direct the order to a broker's broker to obtain better terms for their customer. A broker may only send an order to another broker dealer when the terms obtained for the customer are better than the terms that the broker could have obtained if it executed the customer's order.