Aromatic compounds found in most plants and some insects. Terpenes are responsible for the way cannabis smells, and have been associated with the distinct effects it can produce.

Summary from Wikipedia:

Terpenes are a large and diverse class of organic compounds, produced by a variety of plants, particularly conifers, and by some insects. They often 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.

Terpenes are the major components of rosin and of turpentine produced from resin. The name "terpene" is derived from the word "terpentine", an obsolete form of the word "turpentine". Terpenes are also major biosynthetic building blocks. Steroids, for example, are derivatives of the triterpene squalene.

Terpenes and terpenoids are the primary constituents of the essential oils of many types of plants and flowers. Essential oils are used widely as fragrances in perfumery and traditional medicine, such as aromatherapy. Synthetic variations and derivatives of natural terpenes and terpenoids also greatly expand the variety of aromas used in perfumery and flavors used in food additives. Vitamin A is a terpenoid.

Read more