A brain injury is any injury

Injury

-By cause:*Traumatic injury, a body wound or shock produced by sudden physical injury, as from violence or accident*Other injuries from external physical causes, such as radiation injury, burn injury or frostbite*Injury from infection...

 occurring in the brain

Brain

The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...

 of a living organism. Brain injuries can be classified along several dimensions. Primary and secondary brain injury

Primary and secondary brain injury

Primary and secondary brain injury are ways to classify the injury processes that occur in brain injury. In traumatic brain injury , primary injury occurs during the initial insult, and results from displacement of the physical structures of the brain. On the other hand, secondary injury occurs...

 are ways to classify the injury processes that occur in brain injury, while focal and diffuse brain injury

Focal and diffuse brain injury

Focal and diffuse brain injury are ways to classify brain injury: focal injury occurs in a specific location, while diffuse injury occurs over a more widespread area. It is common for both focal and diffuse damage to occur as the result of the same event; many traumatic brain injuries have aspects...

 are ways to classify the extent or location of injury in the brain. Specific forms of brain injury include:

• Brain damage
  Brain damage
  "Brain damage" or "brain injury" is the destruction or degeneration of brain cells. Brain injuries occur due to a wide range of internal and external factors...
  
  , the destruction or degeneration of brain cells.
• Traumatic brain injury
  Traumatic brain injury
  Traumatic brain injury , also known as intracranial injury, occurs when an external force traumatically injures the brain. TBI can be classified based on severity, mechanism , or other features...
  
  , damage that occurs when an outside force traumatically injures the brain.
• Stroke
  Stroke
  A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
  
  , a vascular event causing damage in the brain.
• Acquired brain injury
  Acquired brain injury
  An acquired brain injury is brain damage caused by events after birth, rather than as part of a genetic or congenital disorder such as fetal alcohol syndrome, perinatal illness or perinatal hypoxia. ABI can result in cognitive, physical, emotional, or behavioural impairments that lead to permanent...
  
  , damage to the brain that occurs after birth, regardless of whether it is traumatic or nontraumatic, or whether due to an outside or internal cause.