Electromagnetic (EM) wavelengths shorter than visible light are referred to as "rays," while those longer are called "waves," primarily due to terminology rather than physical differences. The term "rays" emphasizes the straight-line propagation of light, which aligns with the principles of geometrical optics. In contrast, longer wavelengths like radio waves exhibit a spreading behavior, which is why they are termed "waves." The introduction of microwave frequencies, which are closer to visible light, has led to the adoption of line-of-sight concepts in radio communication. This distinction in terminology reflects the different propagation characteristics of EM radiation across the spectrum.
