The concepts of metacognitive reflection, reflection, and metacognition are distinct but have undergone shifts in meaning as they migrated into medical education. Conceptual clarity is essential to the construction of the knowledge base of medical education and its educational interventions. We conducted a theoretical integrative review across diverse bodies of literature with the goal of understanding what metacognitive reflection is. We searched PubMed, Embase, CINAHL, PsychInfo, and Web of Science databases, including all peer-reviewed research articles and theoretical papers as well as book chapters that addressed the topic, with no limitations for date, language, or location. A total of 733 articles were identified and 87 were chosen after careful review and application of exclusion criteria. The work of conceptually and empirically delineating metacognitive reflection has begun. Contributions have been made to root metacognitive reflection in the concept of metacognition and moving beyond it to engage in cycles of reflection. Other work has underscored its affective component, transformational nature, and contextual factors. Despite this merging of threads to develop a richer conceptualization, a theory of how metacognitive reflection works is elusive. Debates address whether metacognition drives reflection or vice versa. It has also been suggested that learners evolve along on a continuum from thinking, to task-related reflection, to self-reflection, and finally to metacognitive reflection. Based on prior theory and research, as well as the findings of this review, we propose the following conceptualization: Metacognitive reflection involves heightened internal observation, awareness, monitoring, and regulation of our own knowledge, experiences, and emotions by questioning and examining cognition and emotional processes to continually refine and enhance our perspectives and decisions while thoughtfully accounting for context. We argue that metacognitive reflection brings a shift in perspective and can support valuable reconceptualization for lifelong learning.