Level 3
A trading service consisting of everything in Level 2, plus the ability to enter quotes, execute orders, and send information. This service is restricted to NASD member firms that function as registered market makers.
Investopedia Commentary
This allows you to enter bid/ask quotes as the trades are being executed right in front of you. It's the fastest way to execute a trade. Also known as Level III.
Related Links
Electronic Trading Tutorial
See also: Level I, Level II, Market Maker, Nasdaq
Also spelled: Level3, Level III, Level Three