According to the 2012 CFA Level 2 Volume 1 Glossary:
“Brokerage The business of acting as agents for buyers or sellers, usually in return for commissions.
(Level II 2012 Volume 1 Ethical and Professional Standards, Quantitative Methods, and Economics, 6th Edition. Pearson Learning Solutions p. G-4).
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It’s worth remembering that brokerage remains the property of the client i.e. if a broker gets commissions (whether it be in the form of cash, reserach, or somthing else) in return for client brokerage that he/she puts with a particular company, then the underlying client must receive the benefit of that brokerage. There are plenty of examples of this in the CFA text, and it is a very important topic, so I suggest you go over as many questions/examples as you can in this area.
Hope that helps!