Shortening is a type of solid fat that is made from vegetable oils, such as soybean and cottonseed oil. Shortening seems to get its name from the fact that it shortens gluten strands in wheat by adding fat. Since it is 100%, as opposed to the 80% fat content of butter or lard, it results in a very tender baked good. It is frequently seen in baking recipes, although it is rarely used in other areas of cooking. Crisco, a popular brand of shortening, was first produced in 1911, and gained popularity because it was reliable, inexpensive (cheaper than butter or lard) and flavorless.
Shortening is made by a process called hydrogenation, which involves add extra hydrogen atoms to the aforementioned vegetable fats and turns them into solids, rather than liquids. This process of turning the previously unhydrogenated oil into a partially hydrogenated fat with trans fatty acids. These days, shortening is made trans-fat free by fully hydrogenating the oils. It tastes exactly the same and functions the same way as the partially hydrogenated shortenings did.
Shortening can be melted or softened and creamed into a mixture. Since it is all fat, it usually produces the most tender and crumbly results in a cake, cookie or pie crust, but it does not have the flavor of butter, nor can it impart the flakiness that butter can give to, for instance, a pie crust.