An order to buy or sell at the current market price. Unless otherwise specified a broker will execute an order as a market order. The advantage of a market order is that if the market is active it will always be executed. The disadvantage is that the price at which it is executed may not be the same as on a real-time quote service or as quoted by the broker. This may be especially true in fast-moving markets where prices are volatile. Also, when an order is placed "at the market" or "at best" for a large number of shares there is a chance that parts of an order will be executed at different prices.