A prism is a three-dimensional solid shape that is bound on all its sides by plane faces. The faces of a prism are flat and identical, except for the top and bottom faces, which are called bases. The other faces of a prism are called lateral faces, and they can be parallelograms, rectangles, or even squares, depending on the shape of the prism. Prisms are named after their base shape, such as a triangular prism or a rectangular prism.

Prisms are a subclass of polyhedrons, which are three-dimensional shapes with flat faces and straight edges). A prism is a polyhedron comprising an n-sided polygon base, a second base which is a translated copy of the first, and n other faces, necessarily all parallelograms, joining corresponding sides of the two bases). All cross-sections parallel to the bases are translations of the bases).

Prisms can be classified based on their shape, type of polygon base, and whether they are regular or irregular. Regular prisms have regular polygons as their bases, while irregular prisms have irregular polygons as their bases.

Prisms have many real-world applications, such as in optics, where they are used to separate white light into its constituent colors. They are also used in architecture and engineering for their strength and stability.