An order (non-displayed order) that is pegged to execute at the floating mid-point of the national best bid and offer (NBBO), with an option to assign limit price by a client. This order can trade with all contra flow irrespective of order size. Upon entry non-displayed mid-point orders are eligible to trade against contra non-displayed midpoint orders and non-displayed limit orders. Such an order is only executed at the NBBO mid-point. And when the national price is locked or crossed, this order is not executable. Potential executions are protected by means such as freeze parameters and bid/ask tick limits. Orders traded at mid-point rounded last sale price and non-rounded last sale price are reported to the public.

This order always provides price improvement of a full trading increment (uptick, downtick), at least, unless the national price spread is one trading increment, in which case, the price improvement will be limited to half a trading increment.

A non-displayed midpoint order is also referred to as a dark midpoint order.