A skin is what makes the appearance of the website. A skin gives your site it's look or style. Skins can be changed to instantly give your site a new look. Skins are made up of the Colors, Backgrounds, Fonts, Image databases, and Border And Margins (all the databases under the 'Design' section on the menu). When saving your website's skin, all the databases and images are saved into one file (called the skin). Skin files can be downloaded and traded with (or sold to) other skinAsite users.
Skins are seperate from the Content and Setup sections. Your site's content is changed using the databases under the 'Content' section on the menu. Changing a skin will not change any of the Setup or Content databases.
See
Skins for more information.