Mayonnaise (mayo) can be described as a thick, creamy sauce or dressing that is made of oil, egg yolks, lemon juice or vinegar, and seasonings. It is used as a condiment. The one that you get in supermarkets, usually lasts up to six months, when kept in the refrigerator. As per the U.S. law, it should contain at least 65% oil by weight, with the exception of reduced-fat and fat-free versions.