Order Book
The real-time record of all outstanding buy and sell limit orders for an asset, organized by price level.
The order book (or limit order book) is the exchange's live ledger of resting buy and sell orders. Bids are stacked below the current price; asks are stacked above. The inside market — the best bid and best ask — is the Level 1 quote.
The depth of the book reveals where large concentrations of buy or sell interest are clustered, which traders use to anticipate support, resistance, and potential price magnets.
Order books are dynamic: orders are added, modified, and canceled hundreds or thousands of times per second in modern markets.
Related Terms
Bid-Ask Spread
The gap between the highest price a buyer will pay (bid) and the lowest price a seller will accept (ask). Crossing it is the minimum cost of an immediate trade.
BeginnerFill
A confirmed execution of an order — the trade happened, shares changed hands at a specific price and time.
BeginnerHidden Order
A limit order whose full quantity is invisible to other market participants — only the fill is reported post-execution.
AdvancedIceberg Order
A large order split so only a small visible portion shows in the order book; the rest is hidden and refreshes automatically as each slice fills.
AdvancedLevel 2 Data
The full order book showing all visible bids and asks beyond the best inside quote, including size at each price level.
IntermediateMarket Depth
The volume of open buy and sell orders at various price levels — a measure of how much size the market can absorb without large price movement.
IntermediateNBBO
The highest bid and lowest ask for a stock across all U.S. exchanges combined — the consolidated quote your broker must benchmark fills against.
IntermediateOdd Lot
Any order for fewer than 100 shares (a round lot). Odd lots are executed differently by some exchanges and historically excluded from certain quotes.
BeginnerOrder Flow
The stream of incoming buy and sell orders hitting the market — analysis of order flow reveals who is aggressive and where price is likely headed next.
AdvancedSlippage
The difference between the expected fill price and the actual fill price. Positive slippage benefits you; negative slippage costs you.
BeginnerTime and Sales
The chronological record of every executed trade in a security — price, size, and timestamp — also called reading the tape.
Intermediate