The least based subset of feminists of all time. It's an acronym for Trans Exclusionary Radical Feminists, but there's nothing radical or feminist about them. Unironic misandrists who don't let their hatred of men stop at just men; they see trans women as villains and trans men as lost lesbian sisters.

a special snowflake who gets triggered by the existence of transgender people and/or men.

Trans-Exclusive “Radical” Feminism. A very outdated, populist-identitarian ideology that defines gender “woman” as a derivative of biological “reality” and is focused on fabricating narratives centered around an enclosed identity (of victimhood). It claims to be radical, but in actuality it is even less radical than liberalism that it criticizes. Overall it’s just pure trash. TERF IS NOT A SLUR. TERF is a fair and appropriate name for a certain tendency. And nobody should take TERFs seriously.

It's an inaccurate label given by gender cultists to women who exclude male people from feminism; women, transmen, nonbinary females, and anyone else who is of the FEMALE SEX, regardless of what they "identity as" is included in radical feminist ideology. It's male-exclusion, not trans-exclusion. Radical feminism is about dismantling a worldwide patriarchy, which thrives on gender ideology and stereotypes, and liberating the female sex. TERFs want to destroy the gender stereotypes of the 1950's to liberate women, while liberal feminists want to enforce them to coddle male feelings.

TERF = Totally Enviable REAL Female 👸
By Deborrah Cooper.

A libtard buzzword used by delusional womanphobic gender switch folks to shame and harras REAL women into silence, for stating basic biology and common sense.

A mild pejorative used to denote Radical feminists who exclude, display hatred and disgust for, and otherwise belittle transgender women on the false and inaccurate claim that they are men, because biological essentialism is actually okay with these "feminists", only as long as it's a cudgel used to shut up those dirty transes.
Internet TERFs may use talking points about how this is a "slur used to silence women and forced upon them by trans people", however, it should be noted that TERFS themselves coined the term TERF, and only pivoted positions when the general public stopped agreeing with them. A slur is a loaded pejorative associated with immutable characteristics. You cannot change being black, gay, trans, etc. and thus, insults directed at someone for being any of these are defined as slurs. TERFism is simply a scientifically incorrect ideology in baldfaced opposition to the American Psychiatric Association among others, and as you can change an ideology or outlook, it is not a slur. There are male TERFs, after all, ideologies aren't exclusive. And by TERF logic, things such as "nazi" "communist" and "liberal" would be slurs as well.