Non-Display orders have a lower execution priority than Subscriber Only or normal visibility orders.TradeStation Help
When you send a non-display order, it will not be reflected in either the Market Depth display or ECN books. For example, stock ABCD is currently 15.00 Bid and offered at 15.25. You are willing to pay 15.15 but are worried the seller, believing there is an interested buyer, will increase his offering price. By placing a 15.15 non-display bid, you will have the opportunity to immediately purchase any stock up to the quantity specified at your limit price or better.
This order will allow you to be filled lower than your limit price since an aggressive seller may come in and offer at 15.05. This Advanced setting is available only with specific order routes.
Non-Display orders have a lower execution priority than Subscriber Only or normal visibility orders.