Traction is a form of friction which descibes how well a tire clings to the driving surface. It is often called grip, and is extremely important for passenger and racing vehicles alike.
Forward & Reverse Traction
Forward traction helps a high-powered vehicle accelerate without spinning the drive wheels too fast (when compared to the speed of the road compared to the vehicle). This also helps the braking performance, making it harder to lock up the brakes, and reducing the stopping distance.
When cornering, side traction keeps a vehicle going around a corner instead of continuing to go forward.
Tires have a given amount of traction available at any given moment. That amount of traction can change due to factors like tire pressure and shifting load, but if all of the available traction is being used for slowing the vehicle down via braking, none is left to change the direction of the vehicle via steering.