A spare part, spare, service part, repair part, or replacement part, is an interchangeable part that is kept in an inventory and used for the repair or refurbishment of defective equipment/units. Spare parts are an important feature of logistics engineering and supply chain management, often comprising dedicated spare parts management systems.

A knock-down kit is a collection of parts required to assemble a product. The parts are typically manufactured in one country or region, and then exported to another country or region for final assembly.