What is a fill or kill order?

Updated 

A fill or kill (FOK) order is an order that is directed to be executed immediately and fully at the market or a specified price or cancelled if not filled. This option can easily be toggled on the CoinDCX web or mobile app interface on the order window. This option is used when the user wants to enter into a position immediately at a specific price. This executes all available opposite orders with that specific price.