I understand.
That was not MY definition.
That was my whimsical interpretation of Judith Butler's definition.

I don't know that I can provide a succinct, "in a nutshell" definition, other than maybe to say,

Any person who, through whatever combination of genetic composition & neurobiology, manifests an insistent, persistent, consistent self-identification with the type of human that societies with a binary gender framework classify as "woman," and who finds it in congruent and, in most cases, damaging (from irksome to unbearable) to be labeled as what societies with a binary framework classify as "man."

For a legal definition, I would add,...
And who was assigned female at birth and has felt no need to alter that classification, or, having not been assigned female at birth, provides through proper legal processes, including letters from a medical doctor and a mental health practitioner, enough evidence of insistent, persistent, consistent self-identification with the type of human societies with a binary gender framework classify as "woman" as to be permitted by a judge to update their gender marker to female.

But the problem with that legal definition is that there are many societies that don't offer a legal recourse, or make it an overly arduous process. And there are many countries (eg: Morocco, Dubai, Indonesia) where simply making one's self-identification as a woman can lead to imprisonment (Dubai), lashings and public shunning (Indonesia), or death (Morocco).