Discount Groups 
You can define more general discounts, that is, discount groups. You can define four different types of discount groups as follows:
For all Business Partners
For a specific customer group
For a specific vendor group
For a specific business partner
In each of the above discount groups' types, you can define any of the following discount groups:
Item group discount
A combination of item properties discount
Item manufacturer discount
Item specific discount
This discount is applied to the price list specified for the business partner in the master record.
Multiple discounts can be defined in any discount groups. For example, if you have defined a discount group for Item groups, you can define in the same discount groups also discounts for manufacturers. Then, in the Business Partner Master Data record or in the Business Partner group definition, you can define the ratio between the different discounts for the effective discount calculation.
In each discount group you can set discount percentage or you can define variable discount according to the bought quantity. You can also set any defined discount group as active or inactive.
To define discount groups, choose 
Inventory 
Price Lists Special Prices Discount Groups 
.
The discount groups are defined on the following tabs:
Item Groups
Properties
Manufacturers
Items