reaction time
The time between seeing the hazard and the brakes being applied.
reaction distance
The distance covered by a vehicle during the reaction time.
Braking distance
The distance covered by a vehicle while bracking.
Stopping distance
The distance travelled while the driver notices a hazard an applies the brakes, and while the vehicle comes to stop.
crumple zone
The parts of the front/back of a car that are designed to collapse during a collision.