Baking chocolate is typically prepared in unsweetened, bittersweet, semisweet and sweet varieties, depending on the amount of added sugar.
Recipes that include unsweetened baking chocolate typically use a significant amount of sugar. Bittersweet baking chocolate must contain 35 percent chocolate liquor or higher. Most baking chocolates have at least a 50% cocoa content, with the remaining content usually being mostly sugar.
Sweet varieties may be referred to as “sweet baking chocolate” or “sweet chocolate”. Sweet baking chocolate contains more sugar than bittersweet and semisweet varieties, and semisweet varieties contain more sugar than bittersweet varieties. Sweet and semisweet baking chocolate is prepared with a chocolate liquor content between 15 and 35 percent.
Info and image from Wikipedia