A customer good will show as a Back Order if there is insufficient stock available to fulfill the order. 

On the Customer Good view page, any back ordered items will appear on the Back Orders table.

The item will show as a Back Order even if there is a partial amount of the customer good available on-hand. 

The order item will remain on back order until a replenishment is done with sufficient stock to fulfill the order item. For more information on replenishment, see Customer Goods - Replenishment.

When the customer good is replenished, any back orders will automatically be fulfilled based on the item order date.