The many meanings of Alzheimer's disease and why they matter for policy, research, and care.

Alzheimer's disease (AD) is a national priority with far-reaching implications for patients, families, clinicians, researchers, and policymakers. Yet the term AD refers to multiple distinct meanings that are often overlooked or ambiguously applied, risking misaligned research and policy priorities that affect patient outcomes. Recent FDA approvals of passive immunotherapies and related biomarker developments show that differing interpretations of AD complicate research, regulatory decisions, payer coverage, and clinical use. In contrast to efforts aimed at revising AD nomenclature, this paper clarifies five key meanings of AD as currently used. It provides a practical framework to indicate how the term AD is applied in different ways within and across clinical, research, regulatory, and policy contexts. Each key meaning-clinical (symptom-focused), genetically determined (mutation-driven), pathological (autopsy-confirmed), plaque-defined (amyloid-beta-plaque-positive), and broad (can encompass multiple dementia types)-may apply alone or in combination depending on context. These distinctions also raise ethical considerations, particularly for biomarker-based diagnoses and their impact on patient communication and decision-making. Using this framework helps decision-makers identify the intended AD meaning and align research, policy, and care for better patient outcomes.