Any unsaturated aliphatic hydrocarbon is a type of organic compound that contains only carbon and hydrogen atoms. The term can refer to three different types of compounds: olefins, ALKENE, and sterols. Olefins are hydrocarbons with a double bond between two carbon atoms, while ALKENE is a hydrocarbon with a double bond between two carbon atoms and sterols are a type of lipid molecule. Poly is a prefix meaning 'MANY' and is used to describe a compound with multiple repeating units.