Also called book, level 2, depth

Order book

The list of resting buy and sell orders at each price. The inside of it is the bid and the ask; the rest is depth, which the free IEX feed does not publish.

Updated 2026-09-16

Every exchange keeps a ledger of the limit orders it is holding: at each price, how many shares are bid for and how many are offered. That ledger is the order book. The two prices in the middle, the highest bid and the lowest ask, are the top of book; everything stacked behind them is depth.

Depth is what a large order eats through. A market buy for more shares than the ask is showing takes the ask, then the next price up, then the next, which is why size moves price and why a thin book is dangerous to trade in size. Reading depth is the skill a DOM trader is selling.

Angie's paper desk shows the inside of the book only. The free IEX feed publishes one venue's best bid and ask with the size at each, and nothing behind them, so the desk draws a book panel and says plainly that there is no ladder. A depth ladder drawn from that data would be invented.

See also

  • Bid-ask spread — The gap between the highest price a buyer will pay and the lowest a seller will accept. It is the cost of trading, and you pay half of it on the way in and half on the way out.
  • Top of book — The best bid and best ask and the size resting at each. It is what a market order trades against, and on one venue it is a sample of the whole market, not the whole market.
  • Time and sales — The running list of executed trades: time, price, size. Reading it is watching who is actually paying up, as opposed to the book, which is what people say they would do.
  • Limit order — An instruction to trade only at a set price or better. It guarantees the price and guarantees nothing about whether you get filled at all.

← See this one in the deck

Educational content, not investment advice. Angie explains how a valuation is built so you can judge it yourself. What you do with that is your call.

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