What is the Difference Between an Essential Oil and a Terpene?

Essential oils are volatile aromatic compounds that exist in individual plants that create the fragrance of the plant. Terpenes are the various, individual aromatic molecules when combine to create an essential oil. In the world of desserts, you can think of an essential oil as the apple pie and the terpenes as the apples, sugar, flour, etc. that collectively come together to make an apple pie.