Cissex, also known as Cissexual, is a sex label to refer to someone whose current and desired sex characteristics match their natural/original sex characteristics. This means that their, genitals, gonads, and other secondary sex characteristics have not been altered through hormone replacement therapy, or surgery, and they have no intention to do so.
Cissex is not the same as cisgender. Transgender people who don’t plan to medically transition would be considered cissex. Additionally, some non-trans people desire different sex characteristics, making them not cissex. It is not necessarily protosex since someone can be cissex and altersex.
The difference between cissex and cisgenital is that one who is cisgenital may or may not want to change other sex traits, such as breasts, while one who is cissex does not desire to change any sex traits. This means that all who are cissex are also cisgenital, but those who are cisgenital are not always cissex.
The opposite of cissex is transsex.
It is unknown when the term was coined, however it has been used amongst the queer community for a number of years.
The flag was coined by Deviantart user FlagsForCisHets on August 8th of 2017. It is based off of the transsex flag, and has no confirmed meaning.