Used in context of general equities. "Can a new customer still participate on opposing side of the trade from that which the first customer initiated?", Inquiring as to whether any portion of that trade is still available See: Open.
Are You Open?
An inquiry as to whether an order to buy or sell a security has been filled. Some orders are only open for a certain amount of time, while some remain open until they are filled. The inquiry can help clarify the matter. See also: IOC, GTC.