Semisweet chocolate falls somewhere between bittersweet chocolate and sweet dark chocolate. This type of chocolate is most commonly used for baking.
Dark chocolate contains chocolate liquor, sugar, and cocoa butter. It also commonly includes lecithin as an emulsifier and vanilla for flavor. Dark chocolate does not contain any milk solids.
Milk chocolate is perhaps the most popular type of chocolate. It actually contains only ten to 40 per cent cacao mixed with sugar and milk. It is much, much sweeter than dark or bittersweet chocolate but isn't great for baking because it's prone to overheating.
Bittersweet chocolate contains 50 percent cocoa. This type of chocolate often has a deeper, more bitter flavor than other types of chocolate.
White chocolate does not contain chocolate liquor or any other cocoa products besides cocoa butter. It doesn't have a very chocolatey taste, but resembles smooth vanilla.