Size is basically the upermontage ECN where market makers can put orders in on the supermontage system to hide their identity while retaining order flow in the nasdaq system instead of routing it to the other ecns such as inca or arca.
SIZE is the same idea as INCA but specific for SuperMontage...any numerous individuals or MMs or whoever can put in orders behind "SIZE" in order to mask their intentions.
My understanding is that most people see SIZE as an aggregate of all orders at a specific price. Is there a way (by subscribing to Totalview for example) where you can view every single order at the same price?