As a Buyer, sometimes the products that you are looking for are all out of stock or unavailable at the moment. However, you still really want to purchase them! Back ordering allows you to purchase the product from the Brand once they are back in stock.
If you have already checked out your products and they are no longer available, cancel the order then message the Brand to let them know that you are still interested and would like to order from them when the products are back in stock. Always remember to communicate with your Brands via Hubba's messaging service!