麦比乌斯带

[ noun ]
a continuous closed surface with only one side; formed from a rectangular strip by rotating one end 180 degrees and joining it with the other end
<noun.artifact>

Mobius strip \M["o]"bi*us strip`\, n. [From August F. M["o]bius,
German mathematician.]
A mathematical object, or a physical representation of it,
which is a two-dimensional sheet with only one surface. It is
constructed or visualized as a rectangle, one end of which is
held fixed while the opposite end is twisted through a 180
degree angle and joined to the fixed end. It is a
two-dimensional object that can only exist in a
three-dimensional space.
[PJC]