Capable of taking up, or of uniting with, certain other elements or compounds, without the elimination of any side product; thus, aldehyde, ethylene, and ammonia are unsaturated; benzene has three unsaturated bonds. The term is applied most commonly to compounds with a double or triple bond between two carbon atoms (as in ethylene).
If the free bonds in a fatty acid chain of carbon atoms are not all occupied by hydrogen atoms, the fatty acid is said to be unsaturated. Oils consisting mainly of the glycerides of unsaturated fatty acids are generally liquid at normal temperatures. (They may be made more solid by hydrogenation which reduces the degree of unsaturation).