School belonging is important for well-being and academic achievement of youth. School belonging is a broad concept for which researchers from different disciplinary backgrounds have developed a variety of synonyms and indicators. To explore the content of the concept of school belonging, an expert rating study was conducted with 73 expert researchers who rated different synonyms, indicators, and clusters of indicators of school belonging. Results showed that the experts considered connectedness the most suitable synonym of school belonging and inclusion, acceptance, connection, and respect the best indicators. With a multidimensional scaling analysis, two dimensions (the object of belonging and the intra- versus interpersonal nature of belonging) and five clusters of indicators were identified. The findings of this study provides some conceptual clarity that may help future research.