Skin is a tissue layer common to most creatures. Different types of creatures have different types of skin. "Normal" creatures (such as domestic creatures Cow, Dog, Cat, large above-ground creatures, etc, for instance) have the skin called Raw hide. Insectoids, like Giant desert scorpion, have the skin called Chitin. Aquatic creatures and reptilians skins, such as Carp, or Dragons are called Scales. Some aquatic creatures may too have the common Raw hide skin (an example is the Whale).
Skins are stored in a refuse stockpile (both fresh and rotten)
 Skin uses
Skins can be tanned. Tanning a skin yields 1 tanned hide. You can't tan Scales, Chitin, or Feathersv0.31.25. The process of tanning raw hides is done at the Tanner's shop. It requires a dwarf with the Tanning labor enabled.
Leather is used to make low-grade armor and clothing. Leather is also used to make bags, quivers, backpacks, waterskins, clothing, shields, armor, crafts and decorations. The process of making and using leather is part of the Meat industry, rather than Clothing industry.