TERF means Trans-Exclusionary Radical Feminist, meaning a person, usually a woman, who in many areas of life has progressive views, but is very Transphobic, especially against Trans Women, and for this reason tends to ally with Trump, Putin, and far-right parties. A prominient example of a TERF is JK Rowling, the author of the Harry Potter novels from the UK.
Here in Hungary my Mom for example is sadly a TERF, and I've read similar opinions from some other Hungarian women on Hungarian-language sites. Basically OK with LGB people as long as they keep to themselves (another somewhat bigoted viewpoint), but declares the existence of Trans Women an attack on their own womanhood.