Julia Serano, author of Whipping Girl, has written a comprehensive post on the terms cis, cissexual and cisgender, which I thoroughly recommend for anyone who is unaware of or uncomfortable with these terms.
“Trans” means “across” or “on the opposite side of,” whereas “cis” means “on the same side of.” So if someone who was assigned one sex at birth, but comes to identify and live as a member of the other sex, is called a “transsexual” (because they have crossed from one sex to the other), then the someone who lives and identifies as the sex they were assigned at birth is called a “cissexual.”
In other words, cissexual people do not experience dissonance between the sex assigned to them at birth in accordance with their physical body, and the gender or ‘subconscious sex’ that they know and feel themselves to be. Crucially, for those who may not have come across the term before, it should be noted that a cis person may dislike the gender stereotypes and roles that are forced on them by patriarchal society, but they do not feel this sense of dissonance between their physical sex (their body) and the sex their brain tells them they are. So while I may not identify with the term “woman” as I have come to understand it in a patriarchal society, I do not feel any internal mental and/or physical rejection of being gendered female, I do not feel that my female body is incongruous with how I gender myself; rather, I have created my own definition of “woman”, and I am happy with that, and with my body. Therefore, I am cis.
The term is important because it places cis and trans people on an equal footing, where terms such as non-trans or normatively gendered posit trans people as an abnormal Other. (And on a purely practical level it’s a hell of a lot quicker than writing “people who are not trans”.) By giving a name to the experience and fact of being cissexual, the term also enables us to recognise and challenge the privileges that cis people benefit from. Serano explains this with reference to the terms homosexuality and heterosexuality:
Fifty years ago, homosexuality was almost universally seen as unnatural, immoral, illegitimate, etc. Back then, people regularly talked about “homosexuals,” but nobody ever talked about “heterosexuals.” In a sense, there were no “heterosexuals”—everyone who wasn’t engaged in same-sex behavior was simply considered “normal.” Their sexualities were unmarked and taken for granted.
If you were lesbian, gay or bisexual (LGB) during this time period, there was almost no way for you to convince the rest of society that you were unfairly marginalized. In society’s eyes, nobody was oppressing you, it was simply your fault or problem that you were “abnormal.” In fact, it was quite common for LGB people to buy into this presumption of abnormality themselves, as there was simply no other obvious way to view their predicament.
But then gay rights activists began challenging this notion. They pointed out that all people have sexualities (not just homosexuals). The so-called “normal” people weren’t really “normal” per se, but rather they were “heterosexual.” And the activists pointed out that heterosexuals weren’t necessarily any better or more righteous than homosexuals. It was just that heterosexism—the belief that same-sex attraction and relationships are less natural and legitimate than heterosexual ones—is institutionalized within society and functions to unfairly marginalize those who engage in same-sex relationships.
She also addresses cis people’s oft-repeated complaint that they don’t identify with the term:
Cis is not meant to be an identity. Rather, it simply describes the way that one is perceived by others.
An analogy: I don’t strongly *identify* with the terms “white” and “able-bodied,” even though I am both of those things. After all, I have been able to navigate my way through the world without ever having to give much thought to those aspects of my person. And that’s the point: It is my white privilege and able-bodied privilege that enables me *not* to have to deal with racism and ableism on a daily basis!
In general, we only identify with those aspects of ourselves that are marked. For example, I identify as bisexual, and as a trans woman, because those are issues that I have to deal with all of the time (because of other people’s prejudices). While I may not strongly identify as white or able-bodied, it would be entitled for me to completely disavow myself from those labels, as it would deny the white privilege and able-bodied privilege I regularly experience.
You can read the rest of the post here, and check out the Cis Privilege Checklist here.