What is the term for the junction point of two nonparallel surfaces of a prism?

The term that best describes the junction point of two nonparallel surfaces of a prism is the "apex." In the context of optics, a prism is a transparent object with at least two nonparallel surfaces that refracts light. The apex is the top point or the peak of the prism where these surfaces meet. This point is critical in understanding how light bends as it passes through the prism, as it indicates the direction in which the light will exit after refraction.

In contrast, the base of a prism refers to the surface that is typically parallel to the ground when the prism is positioned. The edge is where two surfaces meet, which is more general and does not specifically denote the apex's role in light refraction. The vertex usually refers to a point in geometric contexts but is not specifically aligned with the concept of a prism's structure in optical terms. Thus, apex is the most accurate term to describe the intersection of the nonparallel surfaces in a prism.