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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.
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