Traumatic brain injury (commonly referred to as TBI) is sudden physical damage to the brain. The term does not apply to brain injuries that are hereditary, congential or degenerative, or brain injuries induced by birth trauma, toxic substances, or disease-producing organisms.

The American Congress of Rehabilitation Medicine stated that the injury is manifested by one or more of the following:
1. loss of consciousness;
2. memory loss for events immediately before or after the accident;
3. alteration in mental state at the time of the accident (e.g., feeling dazed, disoriented, or confused);
4. focal neurological deficit(s) that may or may not be transient but where the severity of the injury does not exceed the following:
      a. loss of consciousness of approximately 30 minutes or less;
      b. after 30 minutes, an initial Glasgow Coma Scale (GCS) of 13-15; and
      c. posttraumatic amnesia (PTA) not greater than 24 hours.

(Journal of Head Trauma Rehabilitation 8(3), 86-87.)