// GLOSSARY

Partial fill

When only part of your order executes — the book didn't have enough size at your price. The remainder rests, cancels (IOC), or is rejected, depending on order type. Bots must handle partials as the normal case in thin markets, not an edge case.

You asked for 1,000; the book had 350 at your price. What happens to the other 650 depends on your order's time-in-force: a plain limit order leaves the remainder resting; an IOC cancels it; a fill-or-kill (where supported) rejects the whole order rather than fill partially.

Why thin markets make this routine

Prediction-market books frequently show a few hundred contracts per level, so any institutional-adjacent size partials constantly. A bot that assumes "order sent = position acquired" will drift from reality within hours.

Handling it correctly

• Track state per order: sent size, filled size, remaining, average price.
• Reconcile from the venue's fill stream, not from your own intentions.
• Decide the remainder policy explicitly: re-price and re-post, route the rest to the other venue, or stand down.

That remainder decision is exactly what a worked order automates. State-machine patterns for handling partials are in the Python bot guide.