Level 2 data displays the best bid and ask prices (aka "top-of-book") for each market participant (ie various market makers and market centers) in a given security. There are normally many market makers participating in trade matching for a specific stock.
Similar in format to live streaming share prices, a typical Level 2 screen is split in two vertical halves and will show orders on both the bid price of a security (left-hand side) and the offer price (right-hand side).
Level 2 information is of interest to traders and brokers because it indicates the buying and selling pressure behind individual securities.
It's a part of the toolset for most serious traders.
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