A microwave oven (commonly referred to as a microwave) is a kitchen appliance that heats and cooks food by exposing it to microwave radiation. Microwave ovens heat foods quickly and efficiently because excitation is fairly uniform. Microwave ovens are popular for reheating previously cooked foods and cooking a variety of foods. They are also useful for rapid heating of otherwise slowly prepared cooking items, such as hot butter, fats, and chocolate. Unlike conventional ovens, microwave ovens usually do not directly brown or caramelize food, since they rarely attain the necessary temperatures.