Terpenes are a class of natural products consisting of compounds with the formula (C5H8)n for n ≥ 2. They are unsaturated hydrocarbons produced predominantly by plants, particularly conifers, and comprise more than 30,000 compounds. Although sometimes used interchangeably with "terpenes", terpenoids (or isoprenoids) are modified terpenes that contain additional functional groups, usually oxygen-containing. The terms terpenes and terpenoids are often used interchangeably, however. Terpenes are responsible for the aromas, flavors, and even colors associated with various types of vegetation, including cannabis, aromatic herbs like sage and thyme, and citrus fruits. They are thought to protect plants from harsh weather and predators. Terpenes are also the primary constituents of essential oils of many types of plants and flowers, and are important mediators of ecological interactions in plants.

Terpenes are highly aromatic compounds that determine the smell of many plants and herbs, and are an integral part of many alternative therapies, such as aromatherapy. They are bioactive, which means they may affect the body, and produce vibrant smells that form the basis of many essential oils. Limonene is a common terpene that most people can recognize by its scent. It gives the rinds of fruits such as lemons and oranges their citrusy smell and contains therapeutic properties such as anti-inflammatory, antioxidant, and anticancer effects.

In summary, terpenes are a class of natural products consisting of unsaturated hydrocarbons produced predominantly by plants. They are responsible for the aromas, flavors, and even colors associated with various types of vegetation, and are thought to protect plants from harsh weather and predators. Terpenes are also the primary constituents of essential oils of many types of plants and flowers, and are important mediators of ecological interactions in plants. They are bioactive and produce vibrant smells that form the basis of many essential oils.