Significant Order
An order to buy or sell a security that, due to its abnormally large size, has the potential to have a significant effect on a security's price.
Investopedia Commentary
Most significant orders are placed by institutional investors. Since institutional investors know that these large orders can affect share price, they often try to minimize the effects by spreading the orders out over several days or weeks, depending on the size of the order.
Related Links
Institutional Investors And Fundamentals: What's The Link?
See also: Block Order, Block Trade, Elephants, Iceberg Order, Institutional Investor