Fatty acids are made up of a long-chain carbon skeleton that has a carboxylic acid functional group. When three fatty acid molecules attach themselves to glycerol, the resulting molecule is an example of a lipid.
The two fatty acids illustrated below each have a 17-carbon backbone plus the carbon in the carboxylic acid group. Stearic acid is said to be a saturated fatty acid because it has all the hydrogens that can bond to the carbon chain. Linoleic acid is an unsaturated fatty acid, having two double bonds between carbons and therefore has four fewer hydrogens in its structure.
Enger & Ross