The profit factor is the ratio : gross profit / gross loss.
Or the amount of profit in dollar for each dollar spent (lost).
Bigger is the ratio, better it is.
As the demo conditions are softer (less slippage, less busy context, ...) than live trading, it is recommended to spot a minimum profit factor.
This value will depend on your risk management. Let's say that 2 will be a good beginning.
A very big profit factor (like 100, 1000 or more) can be suspicious, if you don't have any loss, that means that you are using a monstruous stoploss. The calculation is then obsolete. And your strategy can be dangerous despite the good ratio.