Pneumocystis pneumonia is a serious respiratory infection caused by the Pneumocystis jirovecii fungus. There are several synonyms for this condition, including Pneumocystosis, PCP, and Pneumocystic carinii pneumonia. The term pneumocystosis is often used to refer to the disease caused by Pneumocystis jirovecii infection. Meanwhile, PCP is commonly used in medical literature to describe Pneumocystis pneumonia. Lastly, Pneumocystic carinii pneumonia is an older term that was used before the Pneumocystis jirovecii organism was identified as the causative agent of this respiratory illness. No matter what term is used, it is important to recognize that Pneumocystis pneumonia is a serious and potentially life-threatening condition that requires prompt medical attention.