"Microwaves are electromagnetic waves with wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz (0.3 GHz) and 300 GHz"
So here you have it:
"A microwave oven (sometimes simply referred to colloquially simply as a "microwave") is a kitchen appliance that heats food by dielectric heating. This is accomplished by using microwave radiation to heat polarized molecules within the food. This excitation is fairly uniform in the outer 1 inch (25 mm) to 1.5 inches (38 mm) inches of a dense (high water content) food item, leading to food being more evenly heated throughout (except in thick dense objects) than generally occurs in other cooking techniques.
"The first commercial microwave oven was developed by Raytheon after World War II from radar technology developed during the war. It was first sold in 1947. Raytheon later licensed its patents for a home-use microwave oven that was first introduced by Tappan in 1955, but these units were still too large and expensive for general home use. The countertop microwave oven was first introduced in 1967 by the Amana Corporation, which had been acquired in 1965 by Raytheon.
"Basic microwave ovens heat foods quickly and efficiently, but, unlike conventional ovens, do not brown or bake food. This makes them unsuitable for cooking certain foods, or to achieve certain culinary effects. Additional kinds of heat sources can be added to microwave packaging, or into combination microwave ovens, to add these additional effects."