They can range from simple retexturing to full-on recreations of certain game aspects. Skins are used almost entirely for cosmetic and aesthetic purposes. Server owners can apply server-side skins which are viewable by anyone who joins the server. Most skins are client-side, meaning that they show up only for the person who has them installed. Skins can be created, downloaded, and installed by players they usually aim to change the materials, textures, or models of a particular aspect of a game such as a weapon or character. Some weapons, such as the Homewrecker, Dalokohs Bar, and Vita-Saw, were originally created as skins and later incorporated into the game by Valve.
Skins are unofficial and not supported by Valve. Skins (commonly referred to as textures) are user modifications that change the appearance of weapons, hats, player models, or any other part of a game.