any of numerous usually colorless, complex, and bitter organic bases containing nitrogen and usually oxygen that occur especially in seed plants

It is the natural occuring substance of a product. They extract the active ingredients in a plant responsible for the given effect. Found primarily in different species of Ephedra, they can include ma huang (Ephedra sinica or Chinese ephedra, a botanical source of ephedrine, pseudoephedrine, and norpseudoephedrine) and Sida Cordifolia (a cousin of ma huang). * Although they (by deffinition) should be all natural, with the big supplement craze, there are non-herbal alkaolids, being created, out there.