The Market Order takes a single parameter:

It will be filled at the best available price. Market orders have slippage protection built-in, meaning that they can only execute within a certain price interval. If a Market Order cannot execute within this interval, the market order will implicitely be converted to a Limit Order. The price of the Limit Order will be the maximum price that fits within the interval (if the order is a buy order), and the minimum price that fits within the interval (if the order is a sell order). The quantity of the Limit Order will be the quantity that is remaining on the Market Order before it is converted.