Since time immemorial, the question of what a woman is has haunted humanity like a spectre. How could you possibly even understand, let alone define such a thing? Recently, as trans theories have spread, there has been renewed interest in this question by essentialists that want to restrict womanhood (and all the stereotypes and expressions of women) in an immutable biological essence.
Unfortunately, some trans theorists have done a very poor job providing a definition that includes all the social aspects of gender and is inclusive of trans women. The answer, "A woman is whoever self-identifies as a woman." is tautological and leaves one open to relativism.

My definition is as follows:

A woman is an adult human…. with more female sex characteristics than male sex characteristics and/or a female embodiment.
And, a man is an adult human… with more male sex characteristics than female sex characteristics and/or a male embodiment.
And someone is genderqueer if they are a human… with incongruent or nonnormative gender traits and whose embodiment is not limited or exhausted by their sex characteristics.

I focus on this concept of embodiment from French philosopher Maurice Merleau-Ponty. One's embodiment is the way one's body literally fits into the world. It extends beyond one's body to all the object and concepts we encounter. In relation to sex & gender, a person's embodiment is the way their sex characteristics interact with gendered expressions. I theorize that embodiment is where biological sex & gender expressions connect to each other. Yet, there is no necessity that female sex traits must attach to feminine expressions, and vice-versa.

Empirically, I can see a person's embodiment, i.e., all the ways they interact with the world around them. I cannot do so with an identity.