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.