"Compassion fatigue" was first introduced in relation to the study of burnout among nurses, but it was never defined within this context; it has since been adopted as a synonym for secondary traumatic stress disorder, which is far removed from the original meaning of the term. The aim of the study was to define compassion fatigue within nursing practice. The method that was used in this article was concept analysis. The findings revealed several categories of compassion fatigue: risk factors, causes, process, and manifestations. The characteristics of each of these categories are specified and a connotative (theoretical) definition, model case, additional cases, empirical indicators, and a denotative (operational) definition are provided. Compassion fatigue progresses from a state of compassion discomfort to compassion stress and, finally, to compassion fatigue, which if not effaced in its early stages of compassion discomfort or compassion stress, can permanently alter the compassionate ability of the nurse. Recommendations for nursing practice, education, and research are discussed.