A polyhedron is a closed, three-dimensional solid bounded entirely by at least four polygons, no two of which are in the same plane. Polygons are flat, two-dimensional figures (planes) bounded by straight sides. A square and a triangle are two examples of polygons.

The number of sides of each polygon is the major feature distinguishing polyhedrons from one another. Some common polygons are the triangle (with three sides), the quadrilateral (with four sides), the pentagon (with five sides), the hexagon (with six sides), the heptagon (with seven sides), and the octagon (with eight sides).

A regular polygon, like the square, is one that contains equal interior angles and equal side lengths. A polygon is considered irregular if its interior angles are not equal or if the lengths of its sides are not equal.

Each of the polygons of a polyhedron is called a face. A straight side that...