One of various liquid, viscid, unctuous, usually inflammable, chemically neutral substances that is lighter than and insoluble in water, but soluble in alcohol and ether and classified as non-volatile. Natural plant oils comprise terpenes and simple esters such as essential oils. Animal oils are glycerides of fatty acids. Mineral oils are mixtures of hydrocarbons. Oils have many uses and include fuels, lubricants, soap constituents, varnishes, etc., and are used as the feedstock for the production of many other products.