The yo-yo is a popular toy made with of a length of string tied at one end to a flat spool. It is used by holding the free end of the string (usually by inserting one finger in a slip knot) and pulling at it so as to cause the spool to turn while it is hanging in mid-air, either winding or unwinding the string. It first became popular in the 1920s.
In the simplest play, the string is wound on the spool by hand. The yo-yo is then thrown downwards, so that it goes down and unwinds the string. It then (by inertia) climbs back, winding the string up. Finally the yo-yo is grabbed, ready to be thrown again. Many other trick plays exist, most based on the basic "sleeper" trick. One of the most famous tricks on the yoyo is "walk the dog". This is done by throwing a strong sleeper and allowing the yoyo to roll across the floor.
English historical names for the yo-yo include bandalore (from French) and quiz. French historical terms include bandalore, incroyable, de Coblenz, emigrette, and joujou de Normandie (joujou meaning little toy).