In geometry, a prism is a three-dimensional shape that has two bases that are parallel and the same size and shape. The prism's sides are all parallelograms. A classic pup tent is a triangular prism.
In optics, a prism is a piece of glass, quartz, plastic, or other material that can be used to refract light. A typical prism is triangular in shape, and when white light (like sunlight) is shown through it, the prism breaks the light into separate colors and displays it as a rainbow (color spectrum). Sir Isaac Newton experimented with prisms in the 1600s, and his work was the beginning of the modern period of both optics and the understanding of light.