There are four classifications of inventory: raw material; work-in-process; finished goods; and maintenance, repair and operating supplies, or MRO goods. One or more of these inventory types are predominately used, depending upon the type of business or firm.
Raw material inventory is that which is used in the fabrication of a finished good that is sold to the consumer. Work-in-process is inventory that is still in production stages and not yet ready for consumer sales. Finished goods are inventory items that are ready for consumer purchase. MRO goods are inventory items that are not for sale but are used in the maintenance and repair of the production machinery.