Background <p>Public health literacy (PHL) is essential for effective engagement in disease prevention and health promotion, yet remains insufficiently defined and poorly measured. A clear conceptual foundation is needed before developing a dedicated PHL assessment tool.</p> Methods <p>We conducted a qualitative abductive study using semi-structured interviews with 31 French public health professionals and expert patients. Data were analyzed through thematic analysis informed by Sørensen’s health literacy skills (access, understand, evaluate, apply) and Freedman’s public health literacy dimensions.</p> Results <p>Findings show that PHL encompasses the ability to access diverse public health information sources; understand public health concepts, epidemiology, prevention tools, policies, and social determinants; critically evaluate information, sources, personal relevance, and personal behaviors; and apply knowledge by disseminating messages and forming intentions to change behavior. Participants emphasized the key role of trusted intermediaries and social networks, while also identifying gaps in PHL among health professionals and policymakers. Cross-analysis revealed alignment with existing models but indicated the need for an additional dimension: communicating and action intention.</p> Conclusion <p>This study refines the conceptual definition of PHL and establishes the empirical foundation for developing a future public health literacy assessment tool focused on prevention and health promotion.</p>