Terpene: A hydrocarbon of general formula (C₅H₈)_n, derived biosynthetically from one or more molecules of isopentenyl pyrophosphate and/or dimethylallyl pyrophosphate. Molecules derived from modification of terpenes (such as by oxidation) are called terpenoids or isoprenoids, although the term 'terpene' is often taken to include terpenoids as well. Terpenes and terpenoids are often categorized by the number of apparent isoprene units they contain, even though these molecules are not derived directly from isoprene itself.