Background <p>Medical desert terminology is used inconsistently across rural health, health services research, and health policy. In some studies, it describes structural scarcity of local services. In others, it is used for waiting time, affordability, quality, or sociocultural barriers. This inconsistency blurs three different tasks: defining an underserved place, measuring that place, and explaining why people in the same place experience access differently.</p> Methods <p>This U.S.-anchored critical conceptual review draws together literature on desert terminology, access theory, rural service erosion, and medical mistrust.</p> Results <p>Medical deserts are defined here as structurally underserved places where needed services are locally unavailable, hard to reach, unstable, or difficult to replace after service loss. Institutional credibility and medical mistrust are treated as related explanatory dimensions of realized access. The review presents a heuristic that links structural access and institutional credibility while keeping them analytically distinct, and it outlines a multilevel measurement agenda for structural access, credibility, mistrust, and realized access.</p> Conclusions <p>This distinction may sharpen health equity research and policy by separating service infrastructure from the conditions that make care usable.</p>