An essential oil is any concentrated, hydrophobic liquid (but can be viscous, nearing a solid state depending on its purity) containing volatile aromatic compounds of plant origin. Essential oils are usually lipophilic or oil-loving compounds that usually are not miscible with water. Instead, they can be diluted in solvents like pure 100% ethanol (ethyl alcohol), polyethylene glycols (PEG's), or other oils. Essential oils are naturally high in volatile organic compounds, or VOC's. The term essential indicates that the oil carries distinctive scent of the plant, not that it is an especially important or fundamental substance. Essential oils do not, as a group, need to have any specific chemical properties in common, beyond conveying characteristic fragrances or aromas. They should not to be confused with compounds known as essential fatty acids.
Essential oils are used in perfumes and cosmetics, or for flavorings in foods and drinks, among other industrial uses. Various essential oils have been used medicinally at different periods in history.