Good-till-canceled (GTC) or Day Order Or Normal Orders

Day orders are orders given to your broker that hold true only during the period of the trading day for which the orders have been given. If the order has not been executed on that day, it will not be passed on to the next trading day. Thus they are orders that are only "good until it is canceled" or "good for the day."

For e.g. you place a stop loss order with your broker to sell a stock, if its price reaches to level X. Now, if it does not reach limit X, your broker will not sell the stock.
However, the stop loss order given to your broker will not hold true for the next day. For, even if the stock reaches level X on Day 2, he will not execute the trade till you instruct him to do so again.