A backorder is an order for a product or service that cannot be fulfilled immediately because the necessary inventory is not available. The order will be filled when stock is received. Backorders can occur when demand for a product exceeds the current supply. They can also happen when production delays or other issues prevent a product from being delivered on time. Backorders can cause disruptions in the supply chain and can lead to customer dissatisfaction. Proper planning and communication can help to minimize the impact of backorders.