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.