Cacao v Cocoa
Cacao and cocoa are used so often interchangeably that even vendors disregard any technical differences when naming products. 'Cacao' has traditionally referred to ingredients not processed using heat. 'Cocoa' powder has either been heated or has had ingredients added to transform it into a ready-mix cocoa for drinks or both.
Cacao = natural, more bitter
Roasting helps reduce bitterness and can be employed a different points throughout the production process as a way to soften the bite in cacao's chocolatey flavor.
Alkalization of the cacao will also decrease its bitterness, which is done with a potassium carbonated solution that will neutralize the acidity. This process yields 'Dutched cocoa.' Dutched cocoa is darker in appearance, more soluble in water, and is used in many modern chocolates. NOTE: In baking Dutched cocoa can not be swapped with other powders without accounting for the pH difference. Leavening ingredients in a recipe are usually in proportion to the expected pH of the powder.
Beyond the obvious hot chocolate that can be made using cacao powder mixed with milk and sugar—cacao powder can also be used to make chocolatey smoothies and yogurts or even coffee.
Initial consumption of cacao was done primarily as a liquid in South and Mesoamerica. Even for hundreds of years after it was brought to Europe it continued to be ingested as a drink by the rich and wealthy. It wasn't until 1847 when Joseph Fry, of J. S. Fry & Sons a British chocolate company, formulated a way to make moldable chocolate paste by adding cacao butter back into cocoa powder.