pneumonia Definition

an acute disease that is marked by inflammation of lung tissue accompanied by infiltration of alveoli and often bronchioles with white blood cells (such as neutrophils) and fibrinous exudate, is characterized by fever, chills, cough, difficulty in breathing, fatigue, chest pain, and reduced lung expansion, and is typically caused by an infectious agent (such as a bacterium, virus, or fungus)

pneumonia affecting both lungs

a pneumonia chiefly affecting immunocompromised individuals that is caused by a microorganism (Pneumocystis carinii synonym P. jiroveci), attacks especially the interstitial and alveolar tissues of the lungs, and is characterized especially by a nonproductive cough, shortness of breath, and fever —abbreviation PCP

any of a group of pneumonias (such as Q fever and psittacosis) caused especially by a virus, mycoplasma, rickettsia, or chlamydia

a usually mild pneumonia caused by a mycoplasma (Mycoplasma pneumoniae) and characterized by malaise, cough, and often fever