Pneumothorax is a condition where air enters the pleural space (the area between the lung and chest wall), causing the lung to collapse partially or fully. It can occur spontaneously, due to trauma, or as a complication of lung disease. Symptoms include sharp chest pain, shortness of breath, and rapid breathing. The condition can range from mild to life-threatening, depending on the size of the pneumothorax and the underlying cause. Treatment typically involves removing the trapped air to allow the lung to re-expand, which may require observation, a chest tube, or surgery in severe cases.