What does word micro signify in microwave oven?

The word "micro" in microwave oven refers to the use of microwaves, which are a form of electromagnetic radiation with a wavelength range from about one millimetre to one metre. Microwaves are generated by a magnetron, which is a type of vacuum tube, and are then passed through a waveguide, which is a metal tube that guides the microwaves to the food. The microwaves interact with the water molecules in the food, causing them to vibrate and generate heat. This heat is what cooks the food.