It's a contemporary concept of gender that, its proponents claim, was held by some Native American tribes, in which sissy boys who failed the usual tests of manhood (or opted out of them) got to live as women, dressing as women and doing women's work. Instead of men, the current version of things refers to them as being "two-spirit"—female souls in male bodies.
In the past, it was referred to by historians and anthropologists as "berdache," the term early French explorers used, which referred to the passive partner in homosexual male sex, and was derived from words with meanings such as "slave" or "concubine."
What nobody mentions now (because the concept has been increasingly sanitized for political ends since the 1970s) is that the tribes who practiced this were generally ones where women had extremely low status and were treated as chattel and drudges. So a man who was "two-spirit" wasn't some great mystical tranny medicine woman with a glittery unicorn as a spirit animal; he was an absolute failure of a man in a way that was so shameful he was demoted to being a woman. And women, it should be noted, didn't get elevated to male status by being butch; they were stuck as women. There are accounts of masculine women performing men's roles in some societies, but they're much rarer than men being consigned to the female role.
"Two-spirit," or the berdache tradition, didn't break a gendered binary; it was an expression of black-and-white, binary concepts of gender roles in intensely patriarchal, male-dominated societies.
I normally would have told you to google the term, but the information about it that is currently available has been so whitewashed and twisted to political ends—first by the LGB crowd in the '70s-90s, and then the QT+ retards since the '90s—that all you're going to get is page after page of invented history supporting a specific agenda.
