Hydrogenation is a process used to make oils solid by forcing hydrogen atoms into the polyunsaturated fatty acid molecules that make up oil. Partially hydrogenating oil makes it semi-solid (like butter), while fully hydrogenating oil turns the liquid into a solid (more like beef fat).
Fully hydrogenated fats aren't used very often in cooking because they're solid at room temperature, which makes them difficult to use.
Fully hydrogenated oils can be used for cooking when they're blended with non-hydrogenated polyunsaturated oils to make them softer. Crisco brand shortening contains a mixture of fully hydrogenated oils and regular soybean oil.
Harvard School of Public Health. "Shining the Spotlight On Trans-Fats." http://www.hsph.harvard.edu/nutritionsource/nutrition-news/transfats/.