Prism

—1. A transparent body with, usually, three rectangular plane faces or sides, and two equal and parallel triangular ends or bases; used in experiments on refraction, dispersion, etc. Prisms of different forms are often named from the figure of their bases; as a triangular prism, a quadrangular prism, a rhombic prism. 2. In optics, etc., a piece of transparent refracting material in the form of a prism, usually with three equal rectangular faces and of triangular cro section.