// GLOSSARY

Market order

An order to fill immediately at whatever the book offers, with no price limit. Maximum immediacy, zero price protection — in thin prediction markets it can sweep several levels and fill far from the quote. Prefer marketable limits or IOC with a cap.

A market order says "fill me now at any price." On a deep, liquid book that's nearly harmless; on a prediction-market book showing a few hundred contracts per level, it's how you sweep the book and discover what the fourth price level looks like.

Worked example

The ask shows 200 contracts at 44¢. You market-buy 1,000: 200 fill at 44¢, then 300 at 47¢, then 500 at 52¢ — an average of ~49.9¢ for a market quoted at 44¢. A limit at 45¢ would have filled 200 and left you to decide about the rest.

The safer substitutes

Most careful systems never send true market orders. A marketable limit order (limit set slightly through the touch) or an IOC order with a price cap delivers the same immediacy with a bounded worst case. Some venues implement "market" orders internally as aggressive limits anyway — semantics vary, so check the docs. Why unlimited aggression is uniquely expensive in thin books: slippage in thin prediction markets.