This is a specific resource package used in the server, which adds icons to certain items, such as special horns used in the server, strange mushroom fishing rods that can increase player movement speed, and so on.
A pack that makes things (within reason) 3D, stellarly!
3D doors, 3D trapdoors, 3D ladders, 3D rails, beacon, 3D brewing stand, 3D iron bars, 3D mushrooms, 3D fungi, and more!
It also gives doors proper hinges and sides!