Greed is when someone is not contented (not satisfied and not happy) with what he has and he is willing and eager to have more than that no matter the circumstances. It is the excessive desire or craving for the something more e.g money or something valuable for selfish interests.
Greed motivate someone to work very hard, it encourage them to find more knowledge and skills on trading or whatever they are craving for, it can lead to stress and depression which may harm the health of the person, it also lead to discrimination and conflict, it tarnished someone's image and reputation, greed also lead to loses.