The Iceberg/Reserve attribute, applied through the Display Size field, provides a way to submit large volume orders to the market in increments while publicly displaying only a specified portion of the total order size.
You want to buy 5000 shares of XYZ but want the market to see an order for 200 shares. Make the Display Size column visible by holding your mouse over any order field, clicking the "+" icon and then selecting Display Size from the Quantity group. Enter 200 in the Display Size field and ensure that the order type is a Limit order. The system submits an order for 200, and when that quantity fills another 200 shares are submitted until the entire order fills.
Note that if you use a Market order or if the order is marketable at the limit price, the system will submit up to the total order quantity if it's available and use the Immediate-or-Cancel order attribute.
Note: Any stock or option symbols displayed are for illustrative purposes only and are not intended to portray a recommendation.