The term "microwave" might be a bit misleading when taken literally, as it implies that the wavelength of the radiation is small or "micro" in size. In reality, microwave radiation has wavelengths ranging from about 1 millimeter to 1 meter, which is larger than those of other electromagnetic waves like radio waves but smaller than those of infrared radiation or visible light.
The name "microwave" dates back to the early development of this technology in the 1940s. It was coined due to the use of these electromagnetic waves in the microwave range of the electromagnetic spectrum, which spans from around 300 megahertz (MHz) to 300 gigahertz (GHz). This spectrum also includes other types of waves, like radio waves, but microwaves refer to a specific range within it.
The microwave oven, which is probably the most common application of microwave technology, was invented by Percy Spencer in 1946. The term "microwave oven" was used because it used microwaves to cook and heat food. The name stuck, and since then, the term "microwave" has become synonymous with the kitchen appliance and the technology used in various communication systems, radar, and scientific applications.
In summary, the name "microwave" comes from the range of the electromagnetic spectrum in which these waves operate and has nothing to do with their size being "micro" in the sense of being small. It's simply a historical naming convention that has been widely adopted.