An essential oil is a liquid that is generally distilled (most frequently by steam or water) from the leaves, stems, flowers, bark, roots, or other elements of a plant. Essential oils, contrary to the use of the word "oil" are not really oily-feeling at all. Most essential oils are clear, but some oils such as patchouli, orange and lemongrass are amber or yellow in color.
Essential oils contain the true essence of the plant it was derived from. Essential oils are highly concentrated and a little goes a long way.
Essential oils are not the same as perfume or fragrance oils. Where essential oils are derived from the true plants, perfume oils are artificially created fragrances or contain artificial substances and do not offer the therapeutic benefits that essential oils offer. See the What are Fragrance Oils? article for more information on fragrance oils and why they are not used in aromatherapy.
The chemical composition and aroma of essential oils can provide valuable psychological and physical therapeutic benefits. These benefits are usually achieved through methods including inhalation and application of the diluted oil to the skin.