It is called essential oil, or sometimes plant essence, the concentrated and hydrophobic liquid of volatile aromatic (odoriferous) compounds of a plant. It is obtained by mechanical extraction, steam distillation or dry distillation (Extraction by distillation / Extraction by cold pression / Extraction of the essential oil from the bark / Extraction from whole fruits). Essential oils have been used for thousands of years in the world because of their powerful therapeutic properties, although a little forgotten in the Middle Ages. It is the arrival of the Arabs that will allow a renewal of care by plants. The essential oils then find a place of choice. They were previously used in food and perfumery