Musk is the name originally given to a substance with a penetrating odor obtained from a gland of the male musk deer, which is situated between its back/rectal area. The substance has been used as a popular perfume fixative since ancient times and is one of the most expensive animal products in the world. The name, originated from Sanskrit mu?ká meaning ""testicle,"" has come to encompass a wide variety of substances with somewhat similar odors although many of them are quite different in their chemical structures.