1. An injury to the brain, often resulting from a blow to the head, which can cause temporary disorientation, memory loss, or unconsciousness: The ice hockey leagues are studying changes in helmet requirements because of so many concussions that the players have been experiencing.
2. A damage to an organ of the body which is usually caused by a violent blow, a shaking or some suddenly violent jolting: The automobile accident caused several internal concussions to Mrs. Jackson and so she was unable to continue driving her car anymore.