A market order is an order to buy or sell a security at (spot) current market prices. Whe we say current market price it means the real time price of a security trading in market. This order gets executed immediately as soon as you place it. One of the benefit of a market order is that it guarantees the execution of the order. It means the order will get executed for sure depending upon the price its currently trading. Not to mention, the price at which the order gets executed cannot be guaranteed. The reason is price of a security fluctuates every micro second in market.
As an illustration, suppose current market price of a stock A is Rs 100. You decided to buy 1000 quantity of this share & placed a market order . Your order gets executed immediately. However, there’s no guarantee that the share would be bought at the ‘ask’ price of Rs 100. It might happen that your order get divided in to multiple of total quantity. As a result you would receive a price that is closer to your bid price for eg. 300 quantity at 100.10 ,400 at 100.20 & remaining 300 at 100 . You can see or even calculate your average buying price in your trading terminal.
This happens because the market is volatile in nature: prices fluctuate ever micro second. The latest-traded price also know as LTP in the market may have changed by the time you place (bid) your order. To know more about intraday trading click here .