What distinguishes Co-enzymes from prosthetic groups?

Co-enzymes are  organic compounds associated with apoenzymes.

A prosthetic group is an organic compound bound to the apoenzyme tightly and permanently while a coenzyme associated with the apoenzyme is a transient one usually occurring during the course of catalysis.

 Furthermore, co-enzymes serve as co-factors in a number of different enzymes catalyzed reactions. The essential chemical components of many co-enzymes are vitamins, e.g., the coenzyme nicotinamide adenine dinucleotide (NAD) and NADP contain the vitamin niacin.