CBD is the second most common cannabinoid in Cannabis after THC (Which I talk about here). As opposed to THC, CBD does not get you high and has no psychoactive properties. CBD stands for Cannabidiol.
Also unlike THC, CBD is federally legal in the United States, meaning you can get CBD in any of the fifty states. It is legal to order CBD online as well. (CBD must be derived from industrial hemp plants for it to be legally purchased on a Federal level.)
CBD is most often consumed for its health benefits, which include alleviating pain, anxiety, and cancer symptoms.