Omega-3 fatty acids: A class of essential 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.)

EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are the two principal omega-3 fatty acids. The body has a limited ability to manufacture EPA and DHA by converting the essential fatty acid, alpha-linolenic acid (ALA) which is found in flaxseed oil, canola oil or walnuts.

Omega-3 fish oil is considered a nutraceutical, a food that provides health benefits. Eating fish has been reported, for example, to protect against late age-related macular degeneration, a common eye disease. The American Heart Association recommends eating fish (particularly fatty fish such as mackerel, lake trout, herring, sardines, albacore tuna, and salmon) at least two times a week.

(In technical terms, omega-3 fatty acids have a double bond three carbons from the methyl moiety.)