It is a request made to the broker to execute the requested order as soon as possible or cancel it at once as abbreviated as Immediate Or Cancel.

This option could be followed by a buyer during placing a purchase order. This order allows number of matching shares is possible for the order, and the unmatched portion of the order is cancelled immediately.

These type of order are executed immediately (fully or partially) if matching order is available. If matching orders are not available the order is cancelled.