Definition: Fill or Kill Order (FOK)

Fill or kill (FOK) is a type of time in force order that must be filled immediately, or entirely, or be canceled. They can be filled at the limit price or better, but cannot be only partially filled. 

It is similar in nature to an all or nothing (AON) order, which is commonly used in stock trading. The only fundamental difference between the two orders is that a FOK order focuses on the immediacy of the order being filled or not, while an AON order does not have any time focus. 

FOK is generally used by day traders looking to scalp or take advantage of small price differences over a short duration of time. It is commonly offered on cryptocurrency exchanges, including Bybit. 

They are also used when traders don’t want orders to be partially filled. A trader may place several FOK orders at once, and when one is executed, he or she will then cancel the other orders. 

On Bybit, the FOK order is offered in addition to two other time in force orders: good till cancelled (GTC), and immediate or cancel (IOC). These orders are different to FOK in how they executed.