Terpenes are light aromatic hydrocarbons. The smallest Terpene is called Isoprene and it is made from 5 carbon atoms. Combining multiple isoprene's together you can make up tens of thousands of other Terpenes. These will be multiple isoprene molecules that will have either 10, 15, 20, 25 and 30 carbon atoms. When a Terpene Molecule has a oxygen molecule attached they are classified as a Terpenoid.