Trans-exclusionary radical feminism (TERF), also known as gender-critical feminism, is a subset of feminism that rejects transgender and non-binary identities. Trans-exclusionary radical feminists believe that womanhood is solely defined by sex and that sex is biological, immutable, and binary. They view trans women as men and trans men as women. They consider the concepts of gender identity and gender self-identification to be part of an inherently oppressive "gender ideology", a concept which is shared with the right-wing anti-gender movement.