What is the difference between: a fund manager, a portfolio manager and a trader?
In most companies, a fund and a portfolio mean the same thing; therefore a fund manager and portfolio manager are the same role.
The difference between a portfolio manager and a trader (where exists) is as follows:
Portfolio manager's job is to decide on the best contents (holdings) in the portfolio that would accomplish the portfolio's stated objective within stated constraints (e.g. make the best possible return while keeping the risk under a specified level).
Trader's job at a buy-side institution is to basically execute the trades necessary to change the portfolio holdings from their current state to whatever state portfolio managers decided to achieve.
As a matter of fact, at some smaller buy-side firms (especially fixed income), there ARE no separate trader positions, and portfolio managers do both jobs.
A trader's job is to execute the required trades so that the transaction costs are minimized and the PnL is maximized by buying as low as possible and selling as high as possible (e.g. for a simple example dumping a large chunk of a certain stock all at once would depress the stock price so you would make less money as your average sell price goes down).
Trader's job at a sell-side institution is more involved, as the trader is also responsible for making money for the firm via his trades, e.g. he may trade securities specifically for the purpose of making the money off the trade as opposed to the purpose of achieving desired portfolio composition.
I have always been trader, prop trader and/or market maker in various options and derivatives markets. I have managed my own portfolio with a P&L target under Var & stop loss constraint. But I never called my self PM. The only difference I will see between PM and Trader like I am is that a PM seems not to be executing his own orders on the markets. The role of the broker is to execute orders and advise their clients. I'd like to know more in detail the difference between a trader and a PM myself.