Carob isn't chocolate. It is an evergreen tree with edible legumes that can be made into a cocoa like powder. It does have carbs naturally. It can be used by people allergic to chocolate.

cocoa powder is chocolate minus the cocoa butter (main ingredient in white chocolate) and chocolate liquer.

Baking Chocolate - Pure cocoa liquor with nothing added
Cocoa Powder - Cocoa bean solids; cocoa liquor pressed to remove the cocoa butter
Semisweet Chocolate - Pure cocoa liquor with extra cocoa butter and some sugar
Milk Chocolate - Pure cocoa liquor with extra cocoa butter, sugar and milk solids; more milk than chocolate liquor
White Chocolate - Cocoa butter with sugar and milk; no cocoa bean solids