A market order is an instruction from a trader to a broker to execute a trade immediately at the best available price.
Market orders are the simplest variety of order, with no stipulation of a particular price or timeframe included. For this reason, they are usually executed very quickly – provided there is enough liquidity in the market – and sometimes incur lower commission than other types of order.
With market orders you do not have any control over the price at which your order is filled; your market order will be filled at the then market price which may be significantly worse than the indicative prices visible when placing the order.
If you are happy to trade at or near the current market price, then a market order may be the best option. When a market order has been executed, it is referred to as a ‘filled order’.