Gender is not binary. Myself, I'm neither male nor female in terms of my identity. To simplify it a bit, When I think of myself in my head I don't think of myself as being "a male" or "a female".

Genderqueer and other folks who identify outside the binary often prefer an other option. Trans people who identify as either a woman or man usually answer according to how they identify.

There's people who don't identify as any gender. There's also physically interesexual people[1].

[1]http://en.wikipedia.org/wiki/Intersex

There are people who identify as genderqueer, who don't fit into any gender identity, and people who identify as a gender, who don't have a gender identity.

Damn you, auto-correct. That's "agender."