Market Order

Market Order is an order to buy or sell immediately at the best available price in the market at that time.
The advantage of Market Order is that it will guarantee an execution.
However, the disadvantage of this order is that you cannot control the price at which your order will get executed (or filled), and hence you also won’t know at what price your order will eventually get filled.

Typically, if you are going to buy shares/options, you will pay a price near the Ask Price. If you are going to sell shares/options, you will receive a price near the Bid Price.
However, it is important to note that the last-traded price is not always necessarily the price at which the Market Order will be executed.

When the market is very liquid with very tight bid-ask spreads and not so volatile whereby prices don't change drastically, this kind of order is rather safe.
However, in fast moving & volatile market whereby prices move very fast, or in a less liquid market whereby bid-ask spreads is wide, placing a Market Order can be quite risky, because the price at which the trade got executed (or filled) can deviate significantly from the last-traded price.

When the size of a Market Order is quite big, it is possible that the broker will split the order across a number of participants at the other sides of transaction, resulting in different execution/filling prices for different portion of shares/options.

For the list of other types of order, go to: Types of Orders in Trading.

Related Topics:
* Getting Started Trading
* FREE Trading Educational Videos You Should Not Miss
* Option Greeks
* Understanding Implied Volatility (IV)