Each unsaturated fatty acid has at least one double bond. The omega parameter (ω) tells how many carbons from the end there is a first double bond. As the “end” is taken to be the side where hydrogen is (CH3), and the other side (the carboxyl group COOH) is taken as the beginning (where the chains are linked to triglycerides). The symbol ω (end of the Greek alphabet) expresses the end of the chain (and the symbol α the beginning).
For example, ω − 1 (the end minus 1) means that the double bond is immediately between the first and second carbon atom counting from the end, ω − 3 indicates double bond between the third and fourth. Further in the chain, there may be (PUFA) or may not be (MUFA) additional double bonds. In other words, the parameter ω is the length of a “saturated tail” with single carbon bonds, and this length affects some (physiological) fat properties.