Pneumonia is an inflammation of the air sacs, or alveoli, within the lungs. These sacs may fill with fluid or pus, which severely impairs the oxygen exchange necessary for circulation. The condition can result from various infectious agents, including bacteria, viruses, or fungi. Symptoms often include a productive cough, fever, chills, and difficulty breathing. Diagnosis relies on physical examination and imaging studies, while treatment generally involves antimicrobial medication, supplemental oxygen, or supportive care tailored to the specific cause and severity of the infection.