FOK
Fill-or-Kill — an order type that must be filled in its entirety immediately or cancelled outright.
Definition
A Fill-or-Kill (FOK) order is an order instruction that requires the entire order quantity to be matched at once against resting liquidity. If the book cannot fill the full size at the specified price, the order is cancelled completely. FOK orders never rest on the book, so they are always taker orders.
In practice
On Polymarket's CLOB, FOK orders are the standard choice for market-taking bots that want immediate execution without leaving a partial order open. A poly5m bot placing a taker buy of 100 YES shares at $0.55 sends a FOK order: if fewer than 100 shares are available at or below $0.55, the order cancels and the bot skips the trade. This avoids partial fills that would leave the position undersized relative to the intended Kelly stake.