The translation of this name is actually wrong, because when the name was originally named in German, "Kleinsche Fläche" means "Klein plane". Because the translation problem was written as Flasche, the word means bottle. But it doesn't matter, the word "bottle" is also very appropriate.
In 1882, the famous mathematician Felix Klein (Felix Klein) discovered the famous "bottle" named after him. This is a closed surface like a sphere, that is, a curved surface without edges. But it has only one side. In the picture, we can see that the Klein bottle is indeed like a bottle. But it does not have a bottle bottom, its bottleneck is stretched, and then it seems to pass through the bottle wall, and finally the bottleneck and the bottle bottom circle are connected together. If the bottleneck does not pass through the bottle wall but connects to the bottom ring from the other side, we will get a torus.