You've only got two genders, Male and Female.
You either inseminate the opposite gender with your seed, or you are the gender that gets inseminated with seed. The former produces the DNA component that has a chance for the 23rd chromosome to be a Y, the latter has no change for the 23rd chromosome to be a Y. The former lacks a birthing canal or the ability to give birth, the latter possesses a way to give birth and the means to develop said life that will be brought in to the world.
In the case of those who have for example an aspect of both genders, i.e. having genitals from both genders, other characteristics can identify you. For example, Males often have larger bones, different physique, all in all they also have differently functioning endocrine systems. There are many features that can define a gender, and to be frank they're all biological.
I'm not a fan of all these people judging their genders on how they self identify; you're either Male or Female, there's no middle.
... and the ones that won't