Terpenes are a large group of diverse organic compounds, produced by a different types of plants, particularly conifers, and by some insects. They usually have a strong odor and may protect the plants that produce them by deterring herbivores and by attracting predators and parasites of herbivores. Although sometimes used interchangeably with "terpenes", terpenoids (or isoprenoids) are modified terpenes as they contain additional functional groups, usually oxygen-containing.Terpenes are hydrocarbons.