Discount Groups 
You can define more general discounts, that is, discount groups, for a business partner. You can define one of the following discount groups:
Item group discount
A combination of item properties discount
Item manufacturer discount
This discount is applied to the price list specified for the business partner in the master record.
A discount group for a business partner can only be determined by one of these parameters. For example, if you have defined a discount group for item groups, you cannot define a further group for manufacturers.
To define discount groups, choose 
Inventory 
Price Lists Special Prices Discount Groups 
.
The discount groups are defined on the following tabs:
Item Groups
Properties
Manufacturer