What does the word micro signify in the word micro wave oven?

Answer 1

Micro means very small. Microwaves have much smaller wavelengths than radio waves. In a way, it is an arbitrary name, since microwaves also have a larger wavelength than visible light. But that's how it goes. Someone thought the wavelength was small enough to deserve that name.

Answer 2

The prefix "micro-" in "microwave oven" refers to the small wavelength of electromagnetic radiation used to cook food in the oven, which is much shorter than that of radio waves or infrared radiation. It does not refer to the size of the oven itself.