THE KLEIN BOTTLE

In mathematics, the Klein bottle is a certain non-orientable- surface, i.e., a surface (a two-dimensional manifold) with no distinct "inner" and "outer" sides. Other related non-orientable objects include the Möbius strip and the real projective plane. Whereas a Möbius strip is a two dimensional surface with boundary, a Klein bottle has no boundary. (For comparison, a sphere is an orientable surface with no boundary.)