means A kitchen appliance that heats food quickly by bombarding it with microwave radiation, which makes water molecules jiggle and warm from the inside out.

from A 20th-century compound of "micro-" (Greek mikros, "small") and "wave," naming electromagnetic waves shorter than ordinary radio waves. The cooking appliance traces to wartime radar work: an engineer named Percy Spencer is said to have noticed a chocolate bar melting in his pocket near a magnetron tube — a tidy story that happens to be reasonably well documented — and the "microwave oven" took its name from the waves that did the melting.