Cisgender
In transgender ideology, the term cisgender (often shortened cis as in cis man or cis woman) stands for a person whose supposed gender identity aligns with their sex, as opposed to transgender people who claim to have a gender identity that contradicts their sex. Since feminists oppose the gender essentialist notion of an inborn gender identity, they consequently disagree with the concept of cisgender as defined by transgender ideology.
A simplistic interpretation of cis, often used to defend the term from its opponents, is "anyone who isn't trans." This defense fails to take into account precise definition of trans under transgender ideology, which rests not on the material state of being transsexual, but solely on the concept of gender identity, which is a core tenet the ideology.