Natural/Alkalized Cocoa Powder is a powder which is obtainer from cocoa solids, one of the two components of chocolate liquor.
Chocolate liquor is a substance which is obtainer during the manufacturing process which turns cocoa beans into chocolate products.
Natural/Alkalized Cocoa Powder can be added to baked goods for a chocolate flavor, whisked with hot milk or water for hot chocolate, and used in a variety of other ways, depending on the taste of the cook.
Most markets carry Cocoa Powder, often with several options available.