It stands for midpoint peg; a type of non-displayed order that is pegged to the average of the National Best Bid (NBB) and National Best Offer (NBO). The price in this order is determined as the less aggressive of one minimum price variant (MPV), i.e., $0.01 for most stocks, lower than the NBB for buy orders (or higher than the NBO for sell orders) or the order’s limit price. The order combines specific features of multiple orders including primary peg order and discretionary order types.

This order, that reflects the trading interest of a retail investor, is priced to trade at the midpoint on entry.

It is also known as a discretionary peg (D-peg).