Fatty acids are molecules that contain carbon atoms linked in chains. The chain linkages can be either single or double bonds. When all the carbons are bonded by single bonds, it's called a saturated fatty acid. It's called unsaturated when two carbons are bonded together by a double bond. A monounsaturated fatty acid has one double bond in the molecule. If the molecule contains two or more double bonds, it's called a polyunsaturated fatty acid. Monounsaturared fatty acids such as Oleic acid are known to lower cholesterol levels in the body.