Cisgender

Cisgender (from Latin cis- "on the same side" + gender) means non-transgender. A cisgender person is a person who isn't transgender, in that their gender identity matches  gender and sex they were assigned at birth and they don't have gender dysphoria. Being cisgender is an aspect of a person's gender identity. Cisgender women are women who were assigned female at birth (or were born with certain intersex conditions), and who have a woman gender identity. Cisgender men are men who were assigned male at birth (or were born with certain intersex conditions), and who have a man gender identity.

A person need not have a binary gender identity in order to be cisgender. People who were born intersex and who have a nonbinary gender identity can think of themselves as transgender, or as cisgender. Some cisgender intersex people call their gender identity "intersex," or "intergender." Some people of any gender assigned at birth think of their gender identity as cisgender at the same time as being genderqueer, gender nonconforming, or other identities that don't fit within the gender binary. Most cisgender people don't seek a gender transition, but some do. For example, some drag artists who think of themselves as cisgender go on hormone therapy.

History
The word "cisgender" was "coined in 1995 by a transsexual man named Carl Buijs" to mean "non-transgender." He formed the word "cisgender" from the Latin prefix cis-, "on the same side," which is the counterpart of trans-, "across to the other side."

However, there is some evidence that the word "cisgender" has been independently coined at other times by different people. In 1994, the word appeared in the alt.transgendered newsgroup, in a post by Dana Leland Defosse, who doesn't define the term, as though it was already familiar to the readers.

Later, based on the word "cisgender," the word "cissexual" was created. Julia Serano uses both of these words in her book on trans-feminism, Whipping Girl: A Transsexual Woman on Sexism and the Scapegoating of Femininity (2007). Starting around 2006, both words came into use in academic writings by other writers, such as in the field of queer studies.

Cissexual
A person who isn't transsexual. In some contexts, it can be useful to distinguish between cisgender and cissexual, along with distinguishing between transgender and transsexual. This distinction can be useful when talking about nonbinary and gender nonconforming people. Saying that a person is cissexual "emphasizes that someone is not dealing with the medical and legal aspects of a gender transition"; by contrast, "someone who has a nonbinary gender and [is] not dealing with the medical and legal aspects of a gender transition might call themselves a cissexual genderqueer." Some nonbinary people who transition call themselves transsexual, whereas other nonbinary or genderqueer people who don't transition can call themselves cissexual. (For example, Chanda Prescod-Weinstein is an "agender cis-sex woman".) It is possible to be both transgender and cissexual, if gender and sex are considered to be separate aspects of a person. That said, it is a choice for each person what labels they are comfortable with using for themself, and they may find other ways to label their gender.