Period and Volume Discounts 
Use this function if you want special prices to depend on the items and associated price lists, and not directly on the business partners.
If a customer purchases an item, and neither a special price nor a discount group has been defined for the customer or this item, the special prices for the price list apply. This is the price list specified in the business partner master record.
Example
The Watering Can in Garden Price List 8 has a price of $30. However, the price of oil has risen and the manager decides to raise the whole price list by a factor of 1.5 to reflect the higher costs of transporting the inventory to her remote store. The updated price for the Watering Can is now $45.
In reviewing the updated price list, the manager decides that the new prices are quite high for some items. Since she wants to increase sales over the summer, she offers a discount, just for the Watering Can, during July and August, by entering 20 in the Discount column, signifying a reduction of 20%. The price after discount is $36.
Although the Price field in the Period and Volume Discounts window does not show the new price after discount, the item is displayed in blue, which indicates that a discounted price is applied in certain conditions.