It's very easy to assume that Judaism is an exclusively gender-binary religion. Almost all of the common traditional laws are based on the assumed differences between males and females. We see it in assumed gender roles, in liturgy, in proscribed family responsibilities, and in both our secular and religious laws.
If, however, we look just a bit deeper into our sacred texts, we see that a simple male/female binary is not only cumbersome, it's wholly inaccurate. This description from Trans Torah/Rabbi Elliot Kukla starts the conversation that we will continue throughout the summer:
Zachar/זָכָר: This term is derived from the word for a pointy sword and refers to a phallus. It is usually translated as “male” in English.
Nekeivah/נְקֵבָה: This term is derived from the word for a crevice and probably refers to a vaginal opening. It is usually translated as “female” in English.
Androgynos/אַנְדְּרוֹגִינוֹס: A person who has both “male” and “female” sexual characteristics. 149 references in Mishna and Talmud (1st-8th Centuries CE); 350 in classical midrash and Jewish law codes (2nd -16th Centuries CE).
Tumtum/ טֻומְטוּם A person whose sexual characteristics are indeterminate or obscured. 181 references in Mishna and Talmud; 335 in classical midrash and Jewish law codes.
Ay’lonit/איילונית: A person who is identified as “female” at birth but develops “male” characteristics at puberty and is infertile. 80 references in Mishna and Talmud; 40 in classical midrash and Jewish law codes.
Saris/סריס: A person who is identified as “male” at birth but develops “female” characteristics as puberty and/or is lacking a penis. A saris can be “naturally” a saris (saris hamah), or become one through human intervention (saris adam). 156 references in mishna and Talmud; 379 in classical midrash and Jewish law codes.
There's a huge amount of information to unpack here, and we'll be continuing all summer long to do just that, including looking at the legal obligations of each of the genders and what the real-world application of this information is. For now, though, the main point to take from all of this: The male/female binary is not, in any way, the exclusive system of gender classification in traditional Judaism*.
So how did we get to this point, where the assumption has become that only male and female exist? It's a classic example of commonality being equated to superiority. Because male and female are the two most common categories, they were assumed to be "better," rather than "typical." As we have come to understand the complexities of gender more and more in secular society, these Judaic classifications are beginning to appear more and more often and we can clearly see that our ancestors were quite progressive when it comes to gender.
Because, as Ben Bagbag says in Pirkei Avot 5:22:
בן בגבג אומר, הפוך בה והפך בה, והגי בה דכולא בה, ובה תחזי, סיב ובלי בה; ומינה לא תזוז, שאין לך מידה טובה יותר ממנה
Ben Bagbag said: Turn it [Torah] over and turn it over because everything is in it. Look within it and grow old within it; do not move from it, because there is no better attribute for you to have than it.