text: ### Shapes (geometry)
  
  A polygon is plane figure bounded by line segments.
  
  The figure shown above is a regular pentagon. It is a convex five-sided polygon. It is called a pentagon because it has five sides. It is called regular because all sides have equal length and all interior angles are equal.
  
  A polyhedron is a solid figure bounded by plane polygonal faces. Two adjacent faces intersect at an edge and each edge joins two vertices.
  
  The polyhedron shown above is a pyramid with a square base. It has 5 vertices, 8 edges and 5 faces. It is a convex polyhedron.
  
  The figure above is a non-convex polyhedron.
  
  A convex polyhedron is a finite region bounded by planes, in the sense that the region lies entirely on one side of the plane.
  
  A regular shape can be a polygon. A polygon is regular if all of its sides are the same length and all of its angles have the same measure.