A fatty acid that contains more than one double bond (=) between its carbon (-C) atoms which are unsaturated with hydrogen (-H).
Among the polyunsaturated fatty acids (PUFAs), the omega-3 and omega-6 fatty acids are essential as they need to be included in the diet because the human metabolism cannot create them from other fatty acids. These fatty acids use the Greek alphabet to identify the location of the first double bond (=) in the molecule : “omega” marks the last carbon of the carbon chain and “3” (or “6”) indicates that the fatty acid has its first double bond three (or six) carbons away from the “omega” carbon. The double bond position is also abbreviated as “n-3” (or “n-6”).
Scientific abbreviations for fatty acids tell something about their chemical structure. Alpha-linolenic acid (ALA), for example, is abbreviated as “18:3n-3”. The first part (18:3) means that ALA is an 18-carbon fatty acid with three double bonds, while the second part (n-3) indicates that the first double bond is in the n-3 position, which defines it as an omega-3 fatty acid.