Mayonnaise, colloquially referred to as "mayo", is a thick, cold, and creamy sauce commonly used on sandwiches, hamburgers, composed salads, and French fries. It also forms the base for various other sauces, such as tartar sauce, fry sauce, remoulade, salsa golf, ranch dressing, and rouille.

In cooking, a sauce is a liquid, cream, or semi-solid food, served on or used in preparing other foods. Most sauces are not normally consumed by themselves; they add flavor, moisture, and visual appeal to a dish. Sauce is a French word taken from the Latin salsa, meaning salted. Possibly the oldest recorded European sauce is garum, the fish sauce used by the Ancient Romans, while doubanjiang, the Chinese soy bean paste is mentioned in Rites of Zhou in the 3rd century BC.