Background: Recently, a multitude of terms have emerged, especially within North America and Western Europe, which describe identities that are not experienced within the culturally accepted binary structure of gender which prevails within those cultures. As yet, there is no clear single umbrella term to describe such identities and a mixture of words have been used in scholarly work to date. Aims: To explore the origins and track the emergence of newer terms and definitions for identities between, outside and beyond the gender binary, to outline current trends in descriptors within scholarly work and to suggest a term which is wide enough to encompass all identities. Methods: A comprehensive systematic review was made, following the PRISMA guidelines. Several relevant key terms were used to search Web of Science, ScienceDirect, PubMed, and the International Journal of Transgenderism. The descriptions each title gives for identities outside of the binary are extracted for analysis. Results: Several terms have been used over the years to describe identities outside of the binary. "Non-binary" and "genderqueer" are currently mostly used as umbrella terms. However, "gender diverse" is emerging as a more suitable wide-ranging inclusive term for non-male and non-female identities. Discussion: Identity outside of "male" and "female" is an emerging concept which currently has several identifiers and little academic agreement on which is the most pertinent. The two leading descriptors are "non-binary" and "genderqueer." Gender diverse is emerging as a new term which has the aim of including all other terms outside of male and female within it and this article suggests the increase in its use to describe gender identities outside of the binary.
Keywords: PRISMA; gender diverse; gender identity; genderqueer; non-binary; systematic review; transgender.
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