A
person who in one
manner or another crosses
traditional gender boundaries or otherwise
violates gender stereotypes. For example, one might
cross dress, live as the other
gender part time or full time, or have
sex reassignment surgery to make their body resemble the other gender as much as possible, a
transsexual.
This is often used as a blanket term, to refer to the entire range of gender transgressors, but might also be spefically applied to a person who does not truly fit in another of the other "categories", but still violates the gender norms in one way or another.