A market order is a request to buy or sell a security at the best available price in the current market. It is widely considered the fastest and most reliable way to enter or exit a trade and provides the most likely method of getting in or out of a trade quickly. Filling nearly instantaneously. The trade-off, however, is that market orders fill at a price dictated by the market, as opposed to limit or stop order, which provides a trader more control. Using market orders can sometimes lead to unintended, and in some cases, significant costs.