Take a ribbon of paper, twist one end 180 degrees, and attach it to the other end. The resulting surface, called a Möbius strip, has only one side and one edge.
Since its discovery in the 19th century in a purely mathematical context, the Möbius strip has achieved a life of its own independent of mathematics–in the realms of magic, science, engineering, literature, music, film, art, and elsewhere. An object of continuing fascination, it has shown up in all sorts of unexpected settings: as monumental sculptures, knitted scarves and earbands, and glittering pendants; in designs on postage stamps and greeting cards; and as company logos and the ubiquitous symbol for recycling.