a limit order is an order that places a limit on the price you are willing to pay to buy or sell a stock. Thus, a limit order guarantees a price, but whether the trade will get executed remains uncertain. This is because the stock may not reach the price at which the order is placed during the trading day. So suppose you placed a limit order to buy a stock when its trading at 100, you put a price to buy it at 105, however the stock did not reach to that price, so exchange did accepted your traded but the order remain un-executed as the price of the stock did not came up.
