Glossary
Order book
The live queue of unfilled bids and asks on a Polymarket outcome token. Last price is the last print; the book is where the next fill happens.
The order book is the live queue of unfilled limit orders: bids to buy YES (or NO) and asks to sell, stacked by price. Polymarket’s CLOB shows this per outcome token. Last price is only the last print; the book is where the next fill will actually occur.
Depth matters more than the mid. A 50¢ mid with $200 on the offer is not the same market as 50¢ with $80k on each side. Thin books are why long-tail politics can gap eight points on a single whale print while a 15-minute BTC up/down contract barely moves. YES and NO books are linked through the complete-set identity, but they are not one object: you can have a tight YES book and a hollow NO book.
Multi-outcome NegRisk events have a book per listed name, which is why an event page is the right zoom level. Polydata’s screener and market pages surface last price, volume, and large prints. They are not a brokerage ladder. Use them to see which books are real enough to research — then read depth on the venue. Liquidity is that depth plus makers who replace it; spread is the hole at the touch.