A broker typically connects a buyer and a seller and acts as an intermediary for a trade. He takes on no risk and earns a commission for his services. A trader assumes risk from the transaction.
For example, you call a broker on the NYSE and ask where you can buy 50,000 shares of IBM. He asks the crowd. A trader in the crowd says heâll sell you 50,000 shares for $128. You instruct the broker to buy the shares. The broker buys the shares from the trader for $128 and sells them to you for $128. The broker never has any risk in the transaction, and you pay him a commission for his service. The trader on the floor is now short 50,000 shares of IBM and has assumed the risk.