This article examines the conceptual history and contemporary usages of the term “healing.” In response to longstanding definitional ambiguity, reflections are offered on what are termed the diagnostic criteria, nosology, and etiology of healing. First, a summary is provided of how healing has been defined within medicine. Second, the dimensionality of healing is discussed. Third, healing’s putative determinants are outlined. For biomedicine, healing mainly concerns repair of wounds or lesions and is unidimensional. For complementary medicine, by contrast, healing has been defined alternatively as an intervention, an outcome, and a process—or all of these at once—and is multidimensional, impacting multiple systems from the cellular to the psychosocial and beyond. Notwithstanding these usages, a review of medical texts reveals that healing is rarely defined, nor is its dimensionality or determinants described. Persistent lack of critical attention to the meaning of “healing” has implications for medical research and practice.