Skin
A skin is a specific texture for character models.
Different types of skins
Developing company Raven Studios did a decent job in creating the core skin textures for the in game characters. Some skins were touched up, such as some of the skins used in multiplayer.
The company also allowed for players to create custom skins. Using a third party image editor such as Photoshop or GIMP, a player can change the texture element of a specific character, or to create a brand new texture for a custom model. This freedom also allows for players to take advantage of the in game shaders, allowing for unique creations to be implemented into the game.