Fill or kill

It is a condition on how an instruction may be satisfied rather than a type of order in its own right. Complete execution at the stated price or better, on arrival, or nothing. It sits beside two other conditions that answer the same question differently: immediate or cancel takes whatever quantity is available at once and cancels the rest, and an ordinary resting order waits for its price without any all or nothing requirement.

The condition earns its keep when the quantity requested is large relative to the interest resting near the price, because that is the case where a partial fill would leave an exposure nobody chose. In a thin market the same condition makes cancellation the likely outcome, and a run of cancellations reports something about depth at that instant and nothing about the direction of the price.

Two things trip readers up. A killed order is the instruction working as written, not an error and not a rejection by the counterparty on grounds of price. And immediately means a single attempt as the order arrives, defined by the venue, rather than a short window of time in which the order keeps trying. Terminology is inconsistent across the industry: some systems file the condition under time in force, others under a filling policy chosen per order.