Gender and sexually diverse populations remain understudied and under-represented in research. This is attributable not only to significant and ongoing data collection limitations, where large population-based studies fail to ask adequate questions around gender and sexuality, but also due to continuously evolving terminology in this space. This glossary takes a preliminary step in rectifying these issues by defining and clarifying the application and understanding of key terms related to gender, gender identity, expression and sexuality. In doing so, this glossary provides a point of reference for understanding key differences in gender and sexually diverse terminology to (1) help guide researchers and practitioners in the use and understanding of terms and (2) facilitate the utility of more respectful, inclusive and consistent language application across the public health arena.