A Mobius strip or Mobius band is a surface with only one edge and one side.
What sort of practical application might this have? I am glad you asked. Perhaps it can be really useful as an automobile belt. With only 1 side, the wear and tear should be pretty even. Or, if you want to keep your kids busy, have them make one and then start cutting it down the middle. All kinds of cool stuff can happen!
If you glue the edge of one Mobius strip to the edge of another, you get an object that only exists in 4-D space called a Klein Bottle. Check out some 3-D representations at www.kleinbottle.com