An order to buy or sell a security that, because of its size, will likely cause a considerable price fluctuation. The exact size of a significant order varies according to security. For example, a stock with relatively few shares outstanding will likely have a smaller threshold for a significant order than others. Most of the time, significant orders are made by institutional investors. Generally speaking, they try to avoid price fluctuations by splitting significant orders into several parts and filling them over a certain period of time.