What process do microwaves use to heat food?

A microwave oven (commonly referred to as a microwave) is an electric oven that heats and cooks food by exposing it to electromagnetic radiation in the microwave frequency range. This induces polar molecules in the food to rotate and produce thermal energy in a process known as dielectric heating. American engineer Percy Spencer is generally credited with inventing the modern microwave oven after World War II from radar technology developed during the war.

Source: Wikipedia