Level II

Level II is essentially the order book for Nasdaq stocks. When orders are placed, they are placed through many different market makers and other market participants. Level II will show you a ranked list of the best bid and ask prices from each of these participants, giving you detailed insight into the price action.

This is what a Level II quote looks like

This is what a Level II quote looks like

Knowing exactly who has an interest in a stock can be extremely useful, especially if you are day trading.