What is an Immediate-Or-Cancel order?

Updated 

An Immediate-Or-Cancel (IOC) order is one which has to be executed immediately and fully, or as fully as possible and the non-executed parts are deleted right after. This is quite similar to the fill or kill order, with the only difference being in the fill or kill order, the entire quantity has to be filled or the order is cancelled, whereas in IOC, only the quantity that can be executed at that price is executed and the rest of the quantity is cancelled.

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