TERF is an acronym for "trans-exclusionary radical feminist"). It refers to a group of feminists who do not believe that transgender peoples gender identities are legitimate and who are hostile to the transgender community. Most TERFs came to their ideology via second-wave feminism that radicalized into the belief that trans people are a threat to women. The term can be used in broader senses to refer to trans-exclusionary feminists who are not radical, people with a certain kind of trans-exclusionary politics regardless of whether they are radical feminists, or even things that are culturally associated with second-wave feminism in general).

TERFs have deployed dangerous and extreme online tactics like hate campaigns against trans youth, doxxing of trans activists, and even creating their own online forums when they are kicked out of other online spaces. Often the online abuse has made its way into the real world; TERFs are some of the people we’re seeing trying to ban trans athletes and writing inflammatory op-eds for The New York Times.

The term TERF is controversial and is seen as an insult by those at whom it is directed). However, LGBTQ advocates say those who hold such views deny transgender people their full humanity and go against what the medical community today has accepted as scientific fact around gender and sex.