In stock trading, an instruction to fill an order in its entirety at once and, if that cannot be done, to cancel it. No, we have to cancel this order now—it was fill or kill.
fill or kill
and FOK
phr. a broker’s notation advising the stock exchange to fill a stock order or kill it. (The abbreviation is an initialism. Securities markets.) Get rid of this order. It was fill or kill, and it should have been killed yesterday.