There are more differences between cacao and cocoa than just the spelling, at least in how we use the words. The beans come from the Theobroma cacao tree, and the word cacao comes from the Olmec people in what is now Mexico. It's actually thought that the spelling cocoa originated as a mistake that stuck. So the two are technically referring to the same thing, but we generally use cocoa to refer to a more processed chocolate product with added sugar, versus the raw cacao, which has no sugar.