Back Order

ordered merchandise that is not currently in stock but will be supplied in the future

Backorder is a distribution term that refers to the status of items on a purchase order in the event that some or all of the inventory required to fulfill the order is out of stock. This differs from a forward order where stock is available but delivery is postponed for another reason.Different computer systems will handle back orders in different ways. Typically received stock is allocated first to backorders. These orders are then available to be fulfilled in the normal way.
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in retail, an item or order that is not in stock at the present, but is being reordered and will be available at a later time.