Traumatic brain injury or TBI, (also called intracranial injury) occurs when physical trauma injures the brain. TBI is one of two subsets of acquired brain injury (i.e. brain damage that is not congenital.) It can be classified by severity (mild, moderate, or severe), mechanism of injury (closed or penetrating head injury) and other features of the injury (e.g. focal - occurring in a specific location - or diffuse - occurring over a more widespread area.) TBI is a major cause of death and disability worldwide, especially in young people. Major causes include falls, vehicle accidents, and violence. Prevention includes wearing seat belts in cars, helmets when riding bicycles or motorcycles and when participating in some sports.