Below is a portion of the article
What Is a Level III Quote?
A level III quote is pricing information about a security provided by a trading service. It includes the real-time bid price, ask price, quote size, price of the last trade, size of the last trade, high price for the day, and the low price for the day. Level III gives institutions the ability to enter quotes, execute orders, and send information. Because the level III service offers a high level of market depth, it is restricted to registered Nasdaq market makers.