What is "musk" perfumes and colognes?

When you read the ingredients of some perfumes, colognes and perfumes the body, sometimes simply lists of "musk" as one of the ingredients. What is "musk"? What is it?

The Musk is the name originally given to a substance with a pungent odor from a gland of the male musk deer, which lies between the stomach and genitals. The substance was used as a popular perfume fixative since ancient times and is one of the most expensive in the world. The name originated from Sanskrit muska "testicle," has come to encompass a wide variety of substances with similar odors, but many of them are very different in their chemical structures. Included glandular secretions of animals, musk deer, numerous plants emitting similar fragrances, and artificial substances with similar odors. Until the late 19th century the fragrance only obtained from natural sources. Now, the synthesized compounds are used almost exclusively. The organic compound primarily responsible for the characteristic odor of Musk is muscone.

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