Bumper

n.
  1. That which bumps or causes a bump.
  2. Anything which resists or deadens a bump or shock, such as a metal or rubber rim extending from an object; a buffer.
  3. (Motor vehicles) a protective guard device, usually of metal or rubber, attached horizontally to the front or rear of the frame of a vehicle, designed to resist or deaden a bump or shock, and to prevent damage to the main frame of the vehicle in low-velocity collisions.