An individual or firm who solicits futures and options orders, commodity customers, or customer funds on behalf of a futures commission merchant, or FCM.  The terms commodity broker, and futures broker, are synonymous.  Such a commodity broker is also an options broker (options on futures)  An FCM is a brokerage firm registered with the CFTC (Commodity Futures Trading Commission) that has the ability to hold margin funds for clients and facilitate the clearing of trades with futures exchanges.