What is Order Book?
Crypto Glossary Definition
A current list of buy and sell orders for a specific asset on an exchange. Can be used to see if a market has sufficient liquidity to execute a trade at a given price.
Why Order Book Matters
The order book shows every open buy and sell order for an asset at each price level on an exchange, and is the main tool traders use to gauge near-term supply and demand. A "thin" order book with few large orders nearby can mean a single big trade moves the price significantly.
Order Book in Practice
Suppose a trader wants to buy 50 SOL at market price on a centralized exchange and pulls up the order book first to check what she's actually working with. On the sell side, she sees a large cluster of asks stacked just above the current price, meaning plenty of sellers are ready to part with SOL nearby without her order pushing the price up much. But when she checks a smaller, less popular altcoin she'd also been considering, the order book tells a very different story: only a handful of thin orders sit near the current price on both the bid and ask sides. She realizes that placing even a modest market order there would blow through those few nearby orders and land on much worse prices further down the book, a phenomenon known as slippage. Rather than risk that on the illiquid token, she switches to a limit order instead, placing her own bid at a specific price and waiting for a seller to match it rather than accepting whatever price the thin book gives her. This is exactly why experienced traders check the order book's depth before sizing a trade, not just the last traded price shown on the chart, since a healthy-looking price can hide a dangerously thin book underneath it.
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