Plant constituent distilled to produce essential oil.
The aromatic, oxygenated derivitives of terpenes that can be obtained from plants (in our case), usually by distillation. Unlike a fixed oil that has no scent (unless rancid), volatile oils are all scent. (Example: oil of Peppermint.)
Various terpenoids that evaporate easily (they add taste and aroma to many plants).
Concentrated oils from plants used in cosmetics and as antiseptics.