The terms cacao and cocoa are sometimes used interchangeably – there are no hard and fast rules. Technically, cacao refers to the raw, unprocessed pods that come from the actual cacao tree, while cocoa refers to the product made when you shell the pods and ferment, dry, and roast the seeds. (The seeds don’t start to smell chocolatey until they’re fermented.)
With still more processing and the addition of ingredients like sugar, the cocoa turns into actual chocolate. Dark chocolate has the highest cocoa content-typically 70 percent-is the best kind.
The more cocoa it contains, the more health-giving plant compounds it contains. Note: Actual pure cocoa is bitter. Chocolate with high cocoa content (80 percent and above) will be loaded with the healthy stuff but won’t taste nearly as sweet as your typical candy bar.
(source: The Healthiest Meals on Earth by Jonny Bowden, Ph.D., C.N.S.)