Traumatic Brain Injury (TBI)/Concussion is any disruption of brain function resulting from a blow or jolt to the head or penetrating head injury.

A concussion/mild traumatic brain injury (mTBI) is a head injury from a hit, blow, or jolt to the head that:

• Briefly knocks you out (loss of consciousness <30 minutes)
• Makes you feel dazed, like you had your bell rung (alteration of consciousness)
• Affects your ability to remember the event (post traumatic amnesia <24 hours)

This is most common form of TBI.

There are four categories of TBI including mild, moderate, severe, and penetrating.

Source: http://www.army.mil/tbi and http://www.dvbic.org/