According to
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Limit Order : The order refers to a buy or sell order with a limit price. Suppose, you check the quote of Reliance Industries Ltd.(RIL) as Rs. 251 (Ask). You place a buy order for RIL with a limit price of Rs 250. This puts a cap on your purchase price. In this case as the current price is greater than your limit price, order will remain pending and will be executed as soon as the price falls to Rs. 250 or below. In case the actual price of RIL on the exchange was Rs 248, your order will be executed at the best price offered on the exchange, say Rs 249. Thus you may get an execution below your limit price but in no case will exceed the limit buy price. Similarly for a limit sell order in no case the execution price will be below the limit sell price. Market Order : Generally a market order is used by investors, who expect the price of share to move sharply and are yet keen on buying and selling the share regardless of price. Suppose, the last quote of RIL is Rs 251 and you place a market buy order. The execution will be at the best offer price on the exchange, which could be above Rs 251 or below Rs 251. The risk is that the execution price could be substantially different from the last quote you saw. Please refer to Important Fact for Online Investors.