Backorder is an order for a product that is out of stock and cannot be fulfilled immediately. When a customer places an order for a product that is currently unavailable, the seller may choose to either cancel the order or to fulfill the order when the product becomes available again. If the seller opts to fulfill the order later, the order is placed on backorder, and the customer is notified of the delay. Backordering is often used as a way for companies to manage their inventory and to ensure that customers receive products as soon as they become available, even if that is not immediately.