A lot of people have asked this, so here is the answer:

A TERF is a white supremacist whose gateway to white supremacy is anti-trans bigotry, instead of anti-Semitism or anti-Blackness or anti-migration or misogyny. https://twitter.com/PassiveStein/status/1088180062392856577

As with any gateway, many people engaging in this ideology may not be aware of their proximity to white supremacy. This is the standard radicalization pathway that we have seen over and over and over with, for example, anti-Islamic sentiment.

Personally, and I am writing a blogpost on this, I find it is most comparable to how anti-Semitism gateways are used. Often, we see white supremacists exploiting legitimate grievances with the financial systems by turning into an anti-Semitic issue.

White supremacists take legitimately frustrated and class-oppressed people's anger at banks, and carefully plant the seeds of anti-Semitism. They'll point out the irrefutable fact that there exist Jewish people in executive positions in banking and vilely twist this.

TERFs take a legitimate grievance: patriarchal oppression of women and homophobia and turn it into a movement based on systematic exclusion of a specific class of people. This is the redpill.

Anyhow, my upcoming post is about how we need to stop the good-faith engagements with their ideology and start treating like the gateway to white supremacy that it is.