A limit order is the second type of order, after a market order. Whereas a market order tells your broker to just get you into or out of the stock as fast as possible, a limit order specifies a price. So if you place a limit order to buy MSFT at 120.25, your order will only be filled if there is a seller that is willing to part with the shares at that price. If there is never a seller at that price, your order will never be filled.
