Essential oils What are essential oils? An essential oil is a concentrated hydrophobic liquid containing volatile aroma compounds from plants. Essential oils are also known as volatile oils, ethereal oils, aetherolea, or simply as the oil of the plant from which they were extracted, such as oil of clove. An essential oil is "essential" in the sense that it contains the "essence of" the plant's fragrance—the characteristic fragrance of the plant from which it is derived.The term essential used here does not mean indispensable as with the terms essential amino acid or essential fatty acid which are so called since they are nutritionally required by a given living organism. In contrast to fatty oils, essential oils usually evaporate completely without leaving a stain or residue. Essential oils and aromatherapy Essential oils, in particular, are key to aromatherapy and the calming effect that it can provide. Aromatherapy is the art and science of using essential o...