Third gender is a concept in which individuals are categorized, either by themselves or by society, as neither a man or woman. Wikipedia

Individual whose gender identity is not defined as male or female Wikidata

A category (a gender), present in societies which recognize three or more genders, which is neither male nor female; in some societies, the category may contain individuals who are intersex or androgynous, while other societies may categorize transgender people into it. (Compare fourth gender.). Wiktionary