Extra Virgin - 1 percent acidity, best for sauteeing, marinades, salads, dressings.
Virgin - 1-3 percent acidity, usually cheaper than extra virgin
Pure - mixture of refined and virgin/extra virgin oils
Light - very refined oil, has little of the taste that EV has.
AndrewR - Sorry but you're mistaken.. Light olive oil has a much higher smoke point, making it desireable for deep-frying or high heat frying. It is also used in cases such as baking where a heavy olive oil taste is not desired. Extra virgin oil will turn sour and smoke if you heat it too much.