Using the item category group, you group together different material types for item category determination from the SD view. For every material type, you can define a default item category group which is proposed by the SAP System when you create a material master record. For more information on setting default values please refer to the section "Define material type defaults.
In the sales document, the system determines the item category from the item category group of the material and from the sales document type and proposes this item category in the document. You assign item categories to sales order types and item category groups elsewhere. You can find further information on this in the section "Assign item categories".
If you define your own item category groups, the keys should start with the letter Z, since this name convention is kept free in the standard SAP System for this purpose.