Brass is a mineral added in the Nature Update. It was added along with some other minerals, which include Tin and Copper. Brass Ingots must be crafted into required items, which is smelted from Brass Ore mined out of the ground.
Brass can be used to make Brass Fists, which can be put in the hand slot to deal a lot more damage than usual. It can also make brass tools and armor, which are about as strong as iron. It can also be made into instruments which are Trumpets, Trombones, Baritones, French Horns, and Tubas.