A normal-incidence ray, also known as a perpendicular ray, refers to a beam of light that strikes a surface perpendicular to it. There are several synonyms for this terminology, including orthogonal ray, right-angle ray, and ninety-degree ray. This type of ray is essential for determining the characteristics of a surface, such as reflection, refraction, and absorption. It is a vital concept in fields such as optics, physics, and engineering. Understanding the properties of normal-incidence rays is crucial in the development of technology, including the design of optical devices like cameras and microscopes. Mastery of the terminology related to normal-incidence rays is essential for students and professionals in these fields.