Final answer:
In the context of lean manufacturing principles, overproduction, defects, and inventory are all forms of waste (muda), but employee training is not considered waste; it's an investment that can actually help reduce waste.
Step-by-step explanation:
In manufacturing, where lean principles originated, waste (or muda) refers to any activity that consumes resources but creates no value for the customer. Of the options provided: A) Overproduction, B) Defects, C) Inventory, are all considered forms of waste in lean manufacturing. However, D) Employee training is not considered waste but rather an investment into the workforce that can lead to improved quality, efficiency, and productivity. Consistent and effective training can help reduce other forms of waste by preventing defects, improving processes, and reducing the need for excess inventory due to improved skills and understanding among employees.