Musk is a class of aromatic substances commonly used as base notes in perfumery. They include glandular secretions from animals such as the musk deer, numerous plants emitting similar fragrances, and artificial substances with similar odors. Musk was a name originally given to a substance with a strong odor obtained from a gland of the musk deer. 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 originates from the Late Greek μόσχος 'moskhos', from Persian mushk and Sanskrit मुष्क muṣka (lit. 'testicle') derived from Proto-Indo-European noun múh₂s meaning "mouse". The deer gland was thought to resemble a scrotum. It is applied to various plants and animals of similar smell (e.g. muskox) and has come to encompass a wide variety of aromatic substances with similar odors, despite their often differing chemical structures and molecular shapes.

Natural musk was used extensively in perfumery until the late 19th century when economic and ethical motives led to the adoption of synthetic musk, which is now used almost exclusively. The organic compound primarily responsible for the characteristic odor of musk is muscone.

Modern use of natural musk pods occurs in traditional Chinese medicine. TCMs in China, save for specially exempt drugs, use a synthetic version of undisclosed composition created in 1994. The process was given State Science and Technology Progress Award First Class in 2015.