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 opposite of cissex is transsex.