What Is a Backorder? Definition, Causes & Seller Tips [2026]

A backorder is an order placed for a product that is temporarily out of stock but has confirmed incoming supply. In other words, you are selling an item you don’t physically have in your warehouse yet, with the promise to ship it the moment your next shipment arrives. Understanding what a backorder is — and how it differs from being out-of-stock or a pre-order — is essential for any ecommerce seller who wants to keep revenue flowing without frustrating customers.