The Discount Module allows you to create discounts that are not product-specific. In order to define a Discount, you must either be signed in as Admin, or a User who has rights to this module.
The Pricing Module allows markups/discounts for specific Products or Product Trees. Pricing Rules will automatically be generated to Sales Orders once they are established. Discounts, on the other hand, are much more generic and can be added for an entire Sales Order or per line item. Discounts are generally used for one-time or rare promotions, discounts, or miscellaneous items. Pricing Rules are generally used for consistent markups or discounts for specific products or customers.
Discounts can be either a Flat Amount, or a Percentage Rate of an entire order or line item. Discounts are taxable by default, but may be void of tax if desired.