Nomenclature and name of fatty acids
Fatty substances

In addition to their common names, fatty acids have systematic names that are based on their structure. So linolenic acid, the common name for a fatty acid that has a straight chain of eighteen carbon atoms and three double bonds, has the systematic name of “octadeca” (meaning “eighteen”) “trien” (meaning three double bonds) “oic acid”: “Octadecatrienoic acid”. To indicate the positions of the three double bonds, their positions can be indicated by the number of the carbon atom that is nearest to the carboxyl group: Octadeca-9,12,15-trienoic acid. To indicate the configuration of these double bonds, the name can be preceded by cis or trans : cis, cis, cis -Octadeca-9,12,15-trienoic.

Since this is quite a mouthful, there are a number of shorthand...