What do you mean by stop loss?

Stop loss is the price point in either buy or a sell transaction when the stock price is going opposite to what a person wanted it to go. Person A buys stock XYZ for a price of 250 INR and hopes to sell it at higher price of 275 INR. But instead the stock price starts going downwards below 250. So now he is at a loss, coz if he sells below 250 he will incur a loss. Now there has to be a limit as to how much loss he can sustain. This particular limit he sets is the stop loss. So A bought XYZ for 250, set the target of 275 and stop loss of 245. If the stock goes to 275 he earns 25 Rs profit and if the stock goes to 245, he incurs 5 Rs loss.