Common meaning:

Gender and biological sex of a person match.

Hidden meaning of the Equity religion: 

Your gender is normal (Male or Female) and this makes you part of the oppressive gender majority.

Discussion:

The Equityists believe that if you identify as having a normal gender (cisgender) then you are automatically part of the oppressive gender majority.

Everything in the Equity religion is about oppressors and oppressed groups. They don’t believe in individuals, family, community, state, country or humanity. Everything is forced through the group construct, even when it doesn’t fit very well, and this includes gender.

Since the Equity world must be viewed only through an oppressor and oppressed dynamic, it follows that all the people who have matching gender and biological sex are the oppressors, and all those who don’t are the oppressed. By acting as people with normal genders, they are committing violence against those who are other-gendered. 

It is this belief that all normally-gendered people are oppressors, which has caused the Equityists to introduce the word cisgender to replace the word gender.

Cisgender helps the Equityists identify who the oppressors are.