A yo-yo is a toy that's made of a string wound around two connected discs. The trick of a yo-yo is to drop the discs to the end of the string and flick them back up into your hand.
When you learn to use a yo-yo, you can do tricks that involve the spinning discs and the string's tension. A yo-yo expert can "walk the dog," where the yo-yo rolls along the floor like a dog on a leash, or go "around the world," making a wide circle in the air with the yo-yo before snapping it back up the string to her hand. The word yo-yo appeared around 1915, possibly from a language of the Philippines.