A **prism **is a solid whose ends, or bases, are parallel congruent polygons, and whose sides or faces are parallelograms. A straight line moving parallel to itself, its extremities traveling round the outlines of plane figures, generates the prism.

Prisms are named according to the shape of ends of bases. A prism with a square base is called a **square prism** and a prism with hexagonal base is called a **hexagonal prism**. Similarly, when the ends or bases of a prism are parallelogram, the prism is called a **parallelepiped**.

As shown in the figure the sides or faces of the prism are , etc. These faces are parallelograms. If they were rectangles, angle would be and the prism would be a **right prism**. A prism that is not a right prism is called an **oblique prism**. A side of one of these parallelograms of these prisms is called a **lateral edge**.

The **altitude **of a prism is the distance between the planes of the two bases (i.e.). In a right prism, altitude is the same length as a lateral edge and this is not true for an oblique prism.