Omega-9 fatty acids (monounsaturated fats) are considered non-essential because they can be produced by the body from omega-3 and omega-6 fatty acids as needed. Omega-9 fatty acids are the most abundant fats in the body's cells. Consequently, if you don't have enough omega-3s and omega-6s to make omega-9s, you must get omega-9s from your diet.
Oleic acid is the most common type of omega-9 fatty acid in the diet and is a monounsaturated fat. Monounsaturated fats have only one double bond, so they are liquid at room temperature and become solid when chilled. Consuming foods high in monounsaturated fats in the proper amounts is central to a healthy diet.