In a way, butter is actually a type of shortening because the technical definition of shortening is any form of fat or oil. Shortening is made differently than butter, so there are some rather distinct differences between the two. Shortening is generally manufactured with artificial flavors that include butter.
Butter itself is completely natural and used by churning milk until it is made into a solid. Usually shortening is used when baking as opposed to butter which is used for many different culinary purposes. Many people substitute butter for shortening, especially in modern recipes that call for the latter. When comparing the nutritional value of shortening and butter, there are not too many differences considering that they are both high in saturated fat.