How is light defined when it travels as a wave?

Light, when defined as a wave, is referred to as radiation. This term encompasses all electromagnetic waves, which include visible light along with infrared, ultraviolet, radio waves, and more. Radiation describes the process by which energy in the form of electromagnetic waves propagates through space.

In the context of light as a wave, discussing it as radiation highlights its nature of traveling through a vacuum or medium without needing a physical substance to carry it. This wave-like behavior is characterized by various properties, including wavelength and frequency, which relate to how light interacts with matter.

The other concepts presented, such as wavefront, frequency, and reflection, are all related to the wave properties of light but do not define light itself. Wavefront refers to the surfaces over which an oscillation phase is constant; frequency describes the number of cycles of a wave that pass a point in a given amount of time; and reflection pertains to the bouncing back of light when it encounters a surface. Thus, while these terms are integral to understanding the behavior of light waves, they do not encapsulate the broader definition of light traveling as radiation.