trans fat

n. fat that contains a considerable amount of trans fatty acids; trans fatty acids as a group

Trans fat is the common name for a type of unsaturated fat with trans isomer fatty acid(s). Trans fats may be monounsaturated or polyunsaturated.Most trans fats consumed today are industrially created by partially hydrogenating plant oils — a process developed in the early 1900s and first commercialized as Crisco in 1911. The goal of partial hydrogenation is to add hydrogen atoms to unsaturated fats, making them more saturated. These more saturated fats have a higher melting point making them attractive for baking, and extending their shelf-life. Another particular class of trans fats, vaccenic acid occurs in trace amounts in meat and dairy products from ruminants.
See more at Wikipedia.org...