The term likely comes from the strong, unpleasant smell of a skunk's spray, which is sometimes described as "greasy" or "oily".
The actual chemical compound in skunk spray is thiol, a sulfur-containing compound that produces the pungent odor.
What is skunk grease made out of?
"Skunk grease" is a colloquial term and not a real substance. It is not made from anything, as skunks do not produce grease in the way that animals like cows or sheep do.