Fill or Kill
An order to a broker to buy or sell a security or derivative, usually in large quantities, in which investors have a short period of time to partially or completely fulfill the order before it is cancelled. An FOK may be considered the opposite of a good 'til cancelled (GTC) order; it differs from an immediate or cancel (IOC) order because an IOC may only be partially filled, while an FOK must be entirely filled or the whole offer is void. An FOK is considered a type of day order, but has a much shorter time frame. See also: All-or-None Offering.
An order sent to the floor of an exchange, demanding that it either be filled immediately and in full or be canceled.