Klein bottle
~noun
Entry: a surface that is closed in such a way that it is possible to pass from a point on one side to the corresponding point on the opposite side without passing through the surface and that is formed by passing the narrow end of a tapered tube through the side of the tube and flaring this end out to join the other end.
Etymology: Named after German mathematician Felix Klein (d. 1925).
@ Milton-Kindersley Advanced Dictionary