What is the term for the narrow beam of light called?

The term for a narrow beam of light is commonly referred to as a "ray." In the context of physics, a ray represents a straight path along which light travels. This concept is fundamental in the study of optics, as it allows us to visualize and analyze how light interacts with various surfaces and materials.

When considering other terms, "wave" describes the oscillatory nature of light and other forms of electromagnetic radiation, but it does not specifically denote a narrow or focused path. "Beam" is sometimes used interchangeably with "ray," but it typically refers to a broader collection of rays or light spreading out in a larger area. "Line" can suggest a straight path in general but lacks the specific connotation of light's directionality and behavior.

In summary, the term "ray" is used to indicate the precise and directionally focused movement of light, which is essential for understanding various optical phenomena.