a padded helmet worn by people riding bicycles or motorcycles; protects the head in case of accidents
A crash helmet is a helmet that motorcyclists wear in order to protect their heads if they have an accident. A padded helmet, as one worn by bicyclists, motorcyclists, or aviators, to protect the head in case of accident. a very strong hard hat that protects your head, and is worn by racing car drivers, people riding motorcycles etc