A sport, very close to gymnastics, in which all the moves are done on the floor or on a long springy track — rolls, flips, handsprings, somersaults — with no bars, no rings, and no high equipment. In competition it is often called power tumbling, and athletes run down a narrow bouncy strip doing a fast line of flips. Children's gymnastics classes in many countries are called tumbling classes, because that is where you learn to roll and flip safely before anything else. Note that this word is also just the -ing form of the ordinary verb 'tumble' (to fall over, to roll, or — of prices and numbers — to drop fast), so context tells you which one you are looking at: 'tumbling prices' is the everyday verb, 'she does tumbling on Saturdays' is the sport.