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 penetrating odor obtained from a gland of the male musk deer. The substance has been used as a popular perfume fixative since ancient times and is one of the more expensive animal products in the world. The name originates from the Late Greek μόσχος 'moskhos', from Persian 'mushk', from Sanskrit 'muska-s' "testicle", from Latin 'mus' "mouse" (so called, presumably, for resemblance; see muscle). The deer gland was thought to resemble a scrotum. German has Moschus, from a M.L. form of the Late Greek word. Spanish has almizcle, from Arabic al misk "the musk", from Persian. Applied to various plants and animals of similar smell (e.g. musk-ox, 1744) and has come to encompass a wide variety of aromatic substances with similar odors, despite their often differing chemical structures.

MuSK (for Muscle-Specific Kinase) is a receptor tyrosine kinase required for the formation and maintenance of the neuromuscular junction. It is activated by a nerve-derived proteoglycan called agrin.