External damage to the body is usually separated between open wounds and closed wounds; the former punctures the skin and allows blood loss and bacterial intrusion, while the latter can cause severe internal damage but does not puncture the skin.
Any wound that punctures the skin is an open wound; these range from minor: scraped skin and paper-cuts; to severe: knife and gun wounds. Open wounds are dangerous because of the risk of external infection; anything that penetrates the skin brings bacteria with it, and depending on what it punctures inside the body can cause major organ damage with infection or simply piercing trauma.
Any wound that does not puncture the skin is a closed wound; these range from common bruises to internal organ damage from crushing or striking. Closed wounds can be as fatal as open wounds because of the danger of organ damage; it is common for closed wounds to show no other signs of harm except for some pain, while inside an organ has been ruptured. Internal damage is harder to diagnose without a trained professional and can cause harm days after the initial trauma.