Shock is when your camera lens is hit or hits something else with considerable force. If you drop your lens or if someone slams a car door on your lens it will probably cause damage. Sometimes this damage can be repaired by an professional repair shop but it is almost always very expensive. The best way to protect your lens is to carry it (and your camera) in a padded camera bag, and to be aware of your surroundings. If you have your lens (and camera) out of the bag, pay attention to what is around you and be prepared to move your camera, and yourself, out of harm's way.