Features of an Item Category
When you create a new BOM item, you must select an item category for the item. The item category defines the features and functions of an item. The item category determines which specific item data is processed and controls further activities in the system.

If you define an item category for materials with a material type that is kept in stock, stock can be checked automatically.
In Customizing for Production, you define the features of the item category by choosing Bill of Material
® Item Data ® Define item categories. To define an item category, you answer the following questions: