A market order is an order to buy or sell a financial instrument immediately at the best available current price.
In the real market, market orders are filled only if there are willing sellers or buyers. For example, if you attempt to buy large quantity of a stock, it’s possible that there are not enough sellers, in which case your order can be only partially filled or canceled.
On a simulated trading platform such as Stockfuse, market orders are always executed in full size. However, we use a proprietary transaction cost model to account for market impact of large orders.