Common meaning:

Someone who is on your team and works with you for a common cause.

Hidden meaning of the Equity religion: 

Someone from an oppressor group that accepts the blame for the damage others in their group have done. 

Discussion: 

The Equity faithful believe that allies from dominant groups that support them have nothing to contribute. They think that it is impossible for allies to know anything of value since they are part of an oppressor group. The only job an ally has is to make continual penance for the crimes that other members of their group have committed in the past. 

The sins allies are repenting for may have occurred hundreds of years previously, and in some cases may not even be real, but it is not permissible for allies to question the religious narrative. Since allies have no truth, they need to accept without question any claims of damage they receive from members of the oppressed groups. 

No person should be treated like a subhuman and held responsible for what others have done. Each of us has enough of a job being responsible for what we do personally and it is morally wrong to burden people with the actions of others.