Cisgender

Cisgender (often shortened to cis) is the opposite of transgender or cisn’t, meaning someone who identifies as the gender they were assigned at birth. It describes men who were assigned male at birth and women who were assigned female at birth, which still go by these terms. Some intersex individuals who are non-binary may think of themselves as cisgender, though not all do.

Etymology
"Cis" comes from the Latin prefix meaning "on the same side", as in the cis–trans distinction in chemistry. The origin of the term in reference to gender is credited to Carl Buijs, who proposed the term in 1995, and although the word had been used on the internet before 1995, Carl Buijs is the first recorded source to define the term.

Cisgender vs. Cissexual
Cissexual or cissex, is a term based off transsexual/transsex. In some contexts, it can be useful to distinguish between cisgender and cissexual, along with distinguishing between transgender and transsexual. Cissexual can refer to someone who has not changed their bodies through medical interventions, such as hormones and/or surgeries, and does not seek to medically change their body.

This distinction can be useful as it's possible to be transgender and cissexual, meaning one identifies as another gender, but does not wish to medically transition. It is also possible to be cisgender and transsexual. For example, some drag artists and other gender non-conforming individuals may identify as cisgender, but still seek aspects of a gender transition.

Flag
The cisgender flag was created by DeviantArt user FlagsforCisHets on August 4, 2016. It has no confirmed meaning.

Two other flags were created on the same day by the same user. The pink and blue flag is said to have been created as a heterosexual flag by arianod. However, it was posted with the title "Straight/Cisgender" flag. The flag with the white heart was given the same title. It is unclear if these flags were intended as cisgender flags, as heterosexual flags, or as a cisgender heterosexual flags. No additional information is given for either of them.

A fourth flag was created by FANDOM user OMeera on June 8, 2021. The grayscale cisgender flag is depicted using black, and variations of gray. The heterosexual flag uses black and white (grayscale) to contrast with the rainbow flag.

A fifth flag was created by FANDOM user ThunderBrine on November 17, 2021. The cisgender flag is depicted using gray, and well as azure and rose on direct opposite ends on the flag, symbolizing gender isolation from each other, as if the color were to touch, it could be interpreted as gender questioning, or the midway point between identifying as cisgender and transitioning into transgender. There is also a flag with no cisgender symbols on them.