Backorder
A backorder is a customer order accepted but unable to ship because the item is out of stock; the order is held open and filled when inventory arrives. It differs from a lost sale, where the customer cancels or buys elsewhere, and from a stockout, which is the inventory condition that causes both. Backorder volume and aging show how badly supply is trailing demand.
Examples
Aging tells the story: A distributor shows 1,840 units on backorder across 22 lines. About 1,150 units are under a week old with replenishment in transit: normal flow. But 312 units aged past 30 days all trace to one supplier whose lead time doubled without anyone updating the planning system.
Backorder or lost sale: A connector goes out of stock for three weeks. OEM customers with the part designed in wait it out, so that demand backorders at 100%. Web aftermarket buyers cancel within 48 hours, and roughly $18,000 of demand disappears without ever appearing in a backorder report.
Definition
Three terms get blurred. A stockout is the inventory condition: zero available when demand arrives. A backorder is the commercial outcome when the customer agrees to wait. A lost sale is the outcome when they will not. Which one a stockout becomes depends on switching costs: a qualified custom component gets backordered because requalifying a substitute costs more than waiting, while a catalog fastener becomes a lost sale in an afternoon.
Backorders cost more than the delay. There are expediting fees to compress recovery, customer line-down penalties, extra order administration, and the slow erosion of the service reputation that won the business. Track volume and aging together: 500 units backordered for three days is normal flow; 500 units aged six weeks is a broken supply line.
Chronic backorders on the same items are a parameter problem wearing an execution costume. It is usually one of three things: safety stock sized on old demand, a reorder point built on a lead time the supplier no longer honors, or a forecast bias nobody measured. Fix the parameter and the firefighting stops; fix only the order and it returns next cycle.