A polyhedron with two parallel, congruent polygons being its bases and all the other faces being parallelograms.The line joining the centers of the bases is called the axis of the prism. When the axis is at right angles to the base, the prism is called a right prism. In this case, the lateral faces are rectangles. Otherwise, it is called an oblique prism.

A prism is also classified based on the type of its base. It is called a triangular prism when it has triangular bases. Many of the glass prisms used in optical instruments possess this shape. A prism is called a quadrangular prism when it has a quadrilateral base. The cube is a quadrangular prism with square bases and square lateral faces.