Public health research differs from clinical epidemiological research in that its focus is primarily on the population level social and structural determinants of individual health and the interventions that might ameliorate them, rather than having a primary focus on individual-level risks. It is typically concerned with the proximal and distal causes of health problems, and their location within complex systems, more than with single exposures. Thus, epidemiological terms and concepts may have very different implications when used in the context of population health. This paper considers some key differences in relation to terms like 'population', 'baseline', 'control group' 'outcome' and 'adverse effects'. Even the concept of an 'intervention' often needs careful handling. The paper concludes that there is a need for an expanded, and more realistic use of these terms in the population health intervention research context.