Pneumocystis Carinii Pneumonia, also known as PCP, is a serious lung infection caused by the organism Pneumocystis jirovecii. As this term can be difficult to pronounce and is frequently shortened to PCP in medical contexts, there are multiple synonyms used to refer to this condition. Alternatives include Pneumocystis jirovecii pneumonia, PJP, PC pneumonitis, and Pneumocystosis. These terms may be used interchangeably depending on the medical context and the preference of the healthcare provider or caregiver. Regardless of which term is used, early recognition and treatment are essential for a successful outcome.