Fill or Kill (FOK)
An order type that must be executed immediately and completely at a specified price or better, or it is entirely cancelled with no partial fills allowed.
What is Fill or Kill?
A fill or kill (FOK) order instructs a broker or exchange to execute the entire order immediately at the specified limit price or better, or to cancel the entire order if complete execution is not possible at that instant. Unlike a partial fill, FOK orders accept no compromise: either the full quantity is filled immediately, or nothing is executed. This order type is used by traders who need certainty of a complete position and cannot afford partial execution — for example, when a strategy requires a precise quantity to maintain a hedge or to take advantage of a fleeting arbitrage opportunity. FOK orders are distinct from immediate-or-cancel (IOC) orders, which allow partial fills.
Example
An institutional trader places a FOK order to buy 50,000 shares of a stock at $25.00 or better. If the exchange can only match 40,000 shares at that price immediately, the entire order is cancelled rather than partially filled. The trader must then reassess and potentially resubmit at a different price or time.
Source: FINRA — Order Types