Similar to an order being put on "back-ordered", an order can be put in status of "Partially back-ordered" when one or more products within an order are out of stock, and the order also contains items that are in stock (partial fulfillment). Items that are out of stock will be highlighted in red from within the orders detail section.
If an order is in the "Partially back-ordered status", there are two options available to push the order to fulfillment.
1) Create a Warehouse Receiving Order (WRO) to let our warehouse specialists know that you'll be sending more inventory, once received we will auto fulfill the order.
2) Edit the products in the order to remove out of stock items with in stock inventory.