At thick, creamy dressing that's an emulsion of vegetable oil, egg yolks, lemon juice or vinegar and seasonings. Mayonnaise is one of the most versatile cold sauces. It is an abundant commercial product that can also be made easily at home. There are many reduced-fat mayonnaises, ranging from about 25 percent to 50 percent less fat than regular mayonnaise, as well as fat-free mayonnaise.