Any of numerous hydrocarbons (C5H8)n found especially in essential oils, resins, and balsams¹
Terpenes, which are types of aromatic organic hydrocarbons, are the primary compounds that give Cannabis its delicious smell. What many people don’t know is that they’re also found in a wide variety of other plants - from pine trees and lemons, to lavender and mint. In fact, they are the compounds which help to make aromatherapy the useful treatment that it is; lavender, for example, is high in linalool, a terpene that has been proven to reduce anxiety and alleviate symptoms of depression. Linalool is also found in high concentrations in many Cannabis strains known for their relaxing effects, such as Kosher Kush and Purple Urkle. Together with cannabinoids, the terpene content of these flowers helps to amplify these relaxing, sedating effects that they are known for.
That actually brings us to one of the most interesting things about terpenes - they help cannabinoids to better traverse the blood-brain barrier, which means they allow cannabinoids like THC and CBD to affect the brain more efficiently. So, a flower or concentrate that is high in terpenes does not need to have a high THC percentage to achieve the same effect as one that is very high in THC.
Pretty amazing stuff!