A fill or kill (FOK) order is an instruction sent to a broker or directly to a trading venue that must be carried out immediately and in its entirety. If either of those stipulations cannot be met, the order is canceled. No partial or delayed execution of the order is allowed.
Fill or kill orders are seldom used, but when they are issued its typically to buy a large amount of stock. A small change in price can significantly affect large orders, so in these cases a fill or kill order is ideal to protect a trader’s entire position.
Immediate-or-Kill (IOC) orders are more common, as they allow for partial executions of the order to be filled even if the entire order cannot be done.
All-or-Nothing orders are also similar to FOK orders, but instead of being canceled if unable to proceed, they remain good until they can be executed or are canceled.