Chocolate Liquor: The finely ground meat of the cacao bean. When warm, it's a liquid; when cold, a solid.
Cocoa Butter: The naturally occurring fat in cacao beans. It's why chocolate melts in your mouth.
Cocoa Powder: The fine powder made from the cacao bean meat once most of the cocoa butter has been removed.
Couverture: A high-quality chocolate used by professionals that is specially formulated for dipping and coating.
Milk Chocolate: Made from chocolate liquor, cocoa butter, sugar, vanilla, and milk powder. Quality milk chocolate has a minimum of 30 percent cocoa.
Semisweet or Bittersweet Chocolate: Made from chocolate liquor, cocoa butter, sugar, and vanilla. A premium brand of bittersweet will have a minimum of 62 percent cocoa, while semisweet will have less.
Unsweetened Chocolate: Solid chocolate liquor, with no added sugar, that is usually used in cooking.
White Chocolate: White chocolate contains no cocoa liquor, so it isn't really chocolate. A quality brand contains sugar, cocoa butter, milk powder, and vanilla.