In terms of its structure, it is named "all"-"cis"-9,12,15-octadecatrienoic acid. In physiological literature, it is listed by its lipid number, 18:3, and ("n"−3). It is a carboxylic acid with an 18-carbon chain and three "cis" double bonds. The first double bond is located at the third carbon from the methyl end of the fatty acid chain, known as the "n" end. Thus, α-linolenic acid is a polyunsaturated "n"−3 (omega-3) fatty acid. It is an isomer of gamma-linolenic acid (GLA), an 18:3 ("n"−6) fatty acid (i.e., a polyunsaturated omega-6 fatty acid with three double bonds).