A polyunsaturated fatty acid whose carbon chain has its first double valence bond six carbons from the beginning WordNet 3.0 & Open English WordNet

Omega-6 fatty acids are a family of polyunsaturated fatty acids that have in common a final carbon-carbon double bond in the n-6 position, that is, the sixth bond, counting from the methyl end. Wikipedia

Fatty acids with a double bond at the sixth carbon atom from the end of the carbon chain Wikidata

Any polyunsaturated fatty acid having a double bond between the sixth and seventh carbon atoms from the end of the molecule farthest from the carboxylic acid; although they are essential fatty acids, there is evidence that excess levels can cause a number of diseases. Wiktionary

Type of polyunsaturated fatty acid. Wiktionary (translation)