A Balloon is an item that represents a life in Balloon Battle. In Super Mario Kart, these balloons rotate around the kart like Triple Green Shells, but in Mario Kart 64 and onwards, they are tied to the back of your vehicle. They pop one by one if you are hit by an Item or a vehicle using a Star.
Balloons also can vary in color. If you are playing on teams, the balloons are your team's color (red or blue). If you are playing free-for-all, they are random colors. If you steal enough balloons with a Mushroom (only in Mario Kart: Double Dash!! or Mario Kart DS), you can get an array of balloon colors. In Mario Kart DS, at the beginning of the battle, you start with one and must inflate the rest, having four spare balloons to inflate. In this game, if you lose all your ballons, you are eliminated for the rest of the round. In Mario Kart Wii and Mario Kart 7, you have three and play until time runs out. If you lose all your balloons, then you are regenerated again with all three, but you lose a point. In Mario Kart 8, the balloons have a series logo printed on it and competitors can be knocked out before time runs out. After they're out, they are a ghost and can continue to hit players and such until time runs out.