Unsweetened Baking Chocolate
The paste made from ground, shelled, and roasted cocoa beans without sugar or any added ingredient is called chocolate liquor. Chocolate liquor contains no alcohol, so the name is a bit of a misnomer. In its solid form, you know it as unsweetened baking chocolate. It has a harsh taste and is not meant to be eaten by itself.
Sweet Dark Chocolate
This category includes all chocolates, bittersweet and semisweet, that have at least 35 percent chocolate liquor.
The terms bittersweet and semisweet are often used interchangeably since there is no official distinction between them. Generally (but not necessarily), bittersweet chocolate is less sweet than semisweet, because bittersweet often contains more chocolate liquor. Semisweet and bittersweet chocolate are commonly used in baking, but both are also delicious to eat plain.
Sometimes packaging indicates the percentage of chocolate liquor prominently on the label, sometimes not. Although 35 percent is the required minimum, American bittersweet and semisweet chocolates found in the supermarket―such as Hershey's or Baker's―usually contain at least 50 percent chocolate liquor. It's not uncommon to find chocolate liquor contents from 60 percent or more in premium chocolates such as Callebaut and Scharffen-Berger. These have intense chocolate flavor and are excellent in low-fat desserts.
America's favorite snacking chocolate, milk chocolate is often used for making candy bars. Milk chocolate is lighter in color and has a milder, creamier flavor than dark chocolate. It must contain at least 10 percent chocolate liquor, at least 12 percent milk solids, and not less than 3.66 percent butter fat. Because of the milk solids, milk chocolate doesn't substitute for dark chocolate, as it will not give you enough chocolate flavor.
White chocolate is not really chocolate because it does not contain chocolate liquor. It contains cocoa butter, a derivative of chocolate liquor. Look for cocoa butter on the ingredient listing for quality white chocolate; if it contains palm kernel oil, it's white confectionery coating.