A stop loss order allows the trading member to place an order which gets activated only when the last traded price (LTP) of the share is reached or crosses a threshold price called trigger price. For example, you have a sold position in some security whose current price as of now is Rs.500. You would not like to buy the scrip for more than Rs.510 later in case the market goes against you i.e. go up. You would then put a SL Buy order with a Limit Price of Rs.510. You may choose to give a trigger price of Rs.505 in which case the order will get triggered into the market when the last traded price hits Rs.505 or above. In-case of a sl sell order, you may stop your losses beyond Rs.490 if the market falls by giving a limit price of Rs. 490 with a trigger price of Rs.495.