Maintenance, routine and operating [MRO] categories are low value categories which are not an input to the production process, but which are used in support of operations. The term is a subset of indirect materials and represents a level of classification of categories. Examples of MRO categories would be cleaning materials, lubricants, laboratory supplies, spare parts, gaskets and industrial consumables, and in some procurement organisations these categories would not be aggregated as MRO, but managed individually. The reason that they are grouped together is that they have some common characteristics, such as being relatively low value, and maintaining continuity of availability is a key procurement objective. Sometimes the acronym is used to imply maintenance, repair and overhaul, which describes categories which are used to support plant, equipment and machinery. Scheduled overhauls and maintenance campaigns require provisioning of parts and, in most situations, the cost of downtime is greater than the cost of holding inventory, so MRO often implies matching supply and demand at lowest overall total cost.