A microwave oven, commonly referred to as a microwave, is a kitchen appliance that heats and cooks food by exposing it to electromagnetic radiation in the microwave spectrum. This induces polar molecules in the food to rotate and produce thermal energy in a process known as dielectric heating. Microwave ovens heat foods quickly and efficiently because excitation is fairly uniform in the outer of a homogenous (high water content) food item; food is more evenly heated throughout (except in heterogeneous, dense objects) than generally occurs in other cooking techniques.