A microwave oven is a kitchen appliance that heats food by dielectric heating accomplished with radiation used to heat polarized molecules in food. Microwave ovens heat foods quickly and efficiently, because excitation is fairly uniform in the outer 1 inch (25 mm) to 1.5 inches (38 mm) of a dense (high water content) food item; food is more evenly heated throughout (except in thick, dense objects) than generally occurs in other cooking techniques.
Microwave ovens are popular for reheating previously-cooked foods and cooking vegetables. They are also useful for rapid heating of otherwise slowly-prepared cooking items, such as hot butter and fats, and melted chocolate. Unlike conventional ovens, microwave ovens usually do not directly brown or caramelize food, since they rarely attain the necessary temperatures to do so.