A balloon is a device that is filled with a GAS or AIR to make it float in the AIR. The most common gases used to fill balloons are GAS, AIR, HELIUM, and HOTAIR. GAS is a three letter word that stands for a mixture of gases, usually nitrogen, oxygen, and carbon dioxide. AIR is also a three letter word that stands for the mixture of gases that make up the Earth's atmosphere. HELIUM is a six letter word that stands for an inert GAS that is lighter than AIR and is used to fill balloons to make them float. HOTAIR is a six letter word that stands for hot AIR, which is heated AIR that is used to fill balloons to make them rise.