The Red Shell is an item in the Mario Kart series. When launched, it will go towards the nearest racer. If the Red Shell hits a wall, it will get smashed. But, avoiding the red shell can be easy, just hold a Banana, a Green Shell, or Red Shell behind you by holding the item button (left or right on the D-pad for Wii Wheel users.) Another way is to have a Mushroom and zip ahead of your opponent and the Red Shell would hit them instead of you or a star would destroy it.
The Red Shell has appeared in all the Mario Kart games.