(1) ensure menstrual health is prioritised as a unified objective in global health, development, national policy, and funding frameworks, (2) elucidate the breadth of menstrual health, even where different needs may be prioritised in different sectors, and (3) facilitate a shared vocabulary through which stakeholders can communicate across silos to share learning. To achieve these aims, we present a definition of menstrual health developed by the Terminology Action Group of the Global Menstrual Collective. We describe the definition development process, drawing on existing research and terminology, related definitions of health, and consultation with a broad set of stakeholders. Further, we provide elaboration, based on current evidence, to support interpretation of the definition.