Lean manufacturing focuses on value-added flow and the efficiency of the overall system. A part sitting in a pile of Inventory is waste and the goal is to keep product flowing and add value as much as possible. The focus is on the overall system and synchronizing operations so they are aligned and producing at a steady pace.
Lean Manufacturing is a manufacturing philosophy that shortens the time between the customer order and the product build/shipment by eliminating sources of waste. Waste is anything that does not contribute to transforming a part to your customer needs. The seven wastes in manufacturing are over production, producing defective products, inventories, motion, processing, transportation and waiting.