Fish oil, omega-3: A class of fatty acids found in fish oils, especially from salmon and other cold-water fish, that acts to lower the levels of cholesterol and LDL (low-density lipoproteins) in the blood. (LDL cholesterol is the "bad" cholesterol.)
Omega-3 fish oil is therefore thought to be a neutraceutical, a food that provides health benefits. Eating fish has been reported to protect against late age-related macular degeneration, a common eye disease. The maximum benefit appears to be from eating fish once a week.
(In technical terms, omega-3 fatty acids have a double bond three carbons from the methyl moiety.)