Not being in know I just recently learned the term "cisgender". It means that you identify as the gender you were born (leaving aside, for a moment, the more difficult issues of people who aren't born biologically male or female).
Identifying as the gender you were born distinguishes you from transgender, who tend be be born biologically one gender but identify as the other.
The term cis in this context has its origin in organic chemistry. Cis and trans isomerism describes the orientation of parts of a molecule. Cis trans isomerism on wikipedia.
The guy who coined this term, Carl Buijs, a transsexual man from the Netherlands, supposedly had an ingenious moment thinking about chemistry and gender and thought to himself: "Cis is the opposite of trans, ergo cisgender!"
If you detected sarcasm it's because I find this rather exasperating. The fact that this terminology lives on boggles the mind.
So, here you are, trying to get away from traditional gender norms, and what do you do? You invent a term that reinforces the gender binary. That's fucking brilliant. You identify with a sub culture/group of people who deviate from the normative and then define the world as binary, we and them.
This is why it's so hard to talk about sexism and racism, fir example, because people insist they're different things. Dividing the world up in cis and trans conveniently brushes over the very, very complicated biological intersex and people who do not identify as either.
See, this is important. If people are not the equal then we get weird shit like the right to vote for African American males, but not for women, because somehow one makes sense but not the other.