A triangular pyramid is also called a tetrahedron. A polyhedron is called an $n$-gonal pyramid if one of its faces (the base) is an $n$-gon and the other faces are triangles with a common vertex not lying in the plane of the base. The simplest examples of polyhedra are prisms and pyramids. If this surface does not intersect itself, then it is the full boundary surface of some geometric body, also called a polyhedron hence a third point of view: a polyhedron as a geometric body where, for these bodies, 'holes' bounded by a finite number of plane faces are allowed.

From this point of view a polyhedron is a surface made up of polygonal segments. Most of this article is constructed on the basis of a second definition of a polyhedron, in which its faces are polygons, understood as parts of planes bounded by polygonal curves. If by a polygon is meant a plane closed polygonal curve (even if self-intersecting), one arrives at the first definition of a polyhedron. This definition of a polyhedron has different meanings, according to how a These polygons are called the faces, their sides the edges and their vertices the vertices of the polyhedron. The union (in a three- or higher-dimensional space) of a finite number of plane polygons such that: 1) each side of any polygon is simultaneously the side of another (and only one), called adjacent to the first (along this side) 2) from any of the polygons forming the polyhedron it is possible to go to any other by passing to an adjacent and from it, in its turn, to an adjacent, etc. Please see Talk:Polyhedron for further comments.Ģ010 Mathematics Subject Classification: Primary: 52B This page is deficient and requires revision.

Definition of convex in math