Leather can be used to make Armor. Leather Armor is the weakest type of Armor. As of TU12, Leather Armor got a new look. It now looks more realistic with lines, patches, and more. Also, Leather is an item and cannot be placed.
To get Leather, you must kill a Cow. When a cow has been killed, it will drop 0-2 leather.
You can use Leather to craft Leather armor. These are: a Cap, Tunic, Pants, and Boots. Leather is also required to craft a Frame, along with 8 Sticks. As of TU14, Leather is needed to craft a Book.