Parallel light refers to light beams that are all parallel to each other, commonly described in geometrical optics. In wave optics, this concept is represented by a plane wave, which is a uniform wavefront extending infinitely in space. The term can also relate to parallel-polarized light, depending on the specific context of the discussion. Understanding these definitions is crucial for grasping the behavior of light in various optical applications. Overall, parallel light is fundamental in both geometrical and wave optics.