Final answer:
A flail chest is the injury characterized by three or more ribs fractured in two or more places, which results in a segment of the rib cage moving independently from the chest wall.
Step-by-step explanation:
The injury defined by three or more ribs fractured in two or more places is known as a flail chest. This is a serious condition that occurs when a segment of the rib cage breaks due to trauma and becomes detached from the rest of the chest wall. Because of multiple fractures in the rib bones, this causes the affected area to move independently from the rest of the chest, which can lead to severe complications such as impaired breathing.
A pneumothorax involves air in the chest cavity outside the lung, a hemothorax entails blood within the chest cavity, and a rib contusion refers to bruising of the rib area. These conditions, though related to thoracic trauma, do not match the specific description of multiple fractured ribs as seen in flail chest.