1. The strong-smelling secretion made under the
skin of the abdomen of the
male musk deer. Obtained for perfumery, by killing the deer and
cutting out the musk
pod with looks like a very, very hair scrotum. Why anyone would want to use this to enhance their smell is beyond me but it is
said to be useful for the base notes.
2.Similar secretion from muskrat, musk duck, muskox, musk shrew, civet, musk turtle, or your sweaty neighbour, because your perfume company couldn't be bothered to hunt musk deer.
3. Synthetic product that has a similar strong smell and definitely doesn't increase cancer risk.
4. Elon Musk. Probably far more important to the current economy than all of the above, but sadly he can't be used in perfume.