When you try to place an order for higher quantity you might have received a pop up as seen below.

Let us understand what this slicing means. Order Slicing is a technology which splits a single order to multiple orders if the quantity placed in the original order exceeds Exchange prescribed order limits. 

Exchange has fixed maximum quantity that can be placed in a single Order for each derivative contract and this changes from time to time. For example, the maximum quantity that can be placed in Bank Nifty (lot size 15) is, 900 in a single order which represents 60 lots. As per this, if you place an order for 61 lots in a single order i.e for a quantity of 915 (anything above 900), your order should ideally be rejected as it exceeds the threshold fixed by the Exchange. Hence, you will be required to place one order to execute 900 quantities (60 lots) and another order to execute 15 quantities (1 lot)

This means that multiple orders needs to be placed to trade in huge quantities and that might take little extra time. To facilitate quick order placing for the convenience of clients, Order Slicing was introduced. With Order slicing, you may place any quantity, up to a maximum of 15 times of permissible limit, in a single order. In the example of Bank Nifty, you may place up to 13500 nos (900*15)  in a single order. When such an order is placed, the system will receive your order and will automatically slice it to 15 different orders before sending to Exchange. This is called Order Slicing

Any order intended to be placed for a quantity which is 15 times more than Exchange prescribed limit, needs to be split and placed separately. 

It is also important to note that the maximum order quantity limit differs from instrument to another and from time to time. It can be referred from the NSE website here