What is defined as a group of parallel rays of light?

The term that accurately describes a group of parallel rays of light is "beam." A beam of light is a collection of rays that are oriented in the same direction, making it an essential concept in optics. This concept is widely used in various applications, such as optical instruments, lighting design, and even in medical settings like lasers.

A "ray" refers to a single line of light extending in a straight path, but does not encompass the grouping of multiple rays. A "wavefront" is used to describe the crest of a wave, representing a surface over which an oscillation has the same phase, but it does not specifically emphasize the parallel nature of the rays. Lastly, "path" generally refers to the trajectory that light takes, which does not denote the organization or grouping of light rays as a beam does. Thus, the definition of a beam aligns perfectly with the idea of a group of parallel rays.