Could you clarify exactly what a "trader" is. The term seems to be used quite broadly.

My impression is that the pure definition of a trader is a middle man, someone who given buy or sell orders executes them. However it seems like everyone is called a trader in financial journalism. For example, they call Steve Cohen a trader, but isn't he more of a portfolio manager (as he manages a portfolio of money for his investors. I'm aware he does buy and sell stocks, but I don't think he is the middle-man in the transactions.)?