TERF

TERF (, also written terf) is an acronym for trans-exclusionary radical feminist. First recorded in 2008, the term originally applied to the minority of feminists espousing sentiments that other feminists considered transphobic, such as the rejection of the assertion that trans women are women, the exclusion of trans women from women's spaces, and opposition to transgender rights legislation. The meaning has since expanded to refer more broadly to people with trans-exclusionary views who may have no involvement with radical feminism. 
Those referred to with the word "TERF" typically reject the term or consider it a slur; some identify themselves as "gender critical". Critics of the word "TERF" say that it has been used in an overly-broad fashion, in insults, and alongside violent rhetoric. In academic discourse, there is no consensus on whether or not "TERF" constitutes a slur.
Coinage and usage.
Trans-inclusive cisgender radical feminist blogger Viv Smythe has been credited with popularizing the term in 2008 as an online shorthand. It was used to describe a minority of feminists who espouse sentiments that other feminists consider transphobic, including the rejection of the view, predominant in feminist organizations, that trans women are women, opposition to transgender rights, and the exclusion of trans women in women's spaces and organizations. 
Smythe has been credited with having coined the term "TERF", due to a blog post she wrote reacting to the Michigan Womyn's Music Festival's policy of denying admittance to trans women. She wrote that she rejected the alignment of all radical feminists with "trans-exclusionary radfem (TERF) activists". In a 2014 interview with "The TransAdvocate", Smythe said:
While Smythe initially used "TERF" to refer to a particular type of feminist whom she characterized as "unwilling to recognise trans women as sisters", she has noted that the term has taken on additional connotations and that it has been "weaponised at times" by both inclusionary and exclusionary groups. Though contested, the term has since become an established part of contemporary feminist speech.
Writing in "The New York Times" in 2019, feminist theorist Sophie Lewis noted that the term "TERF" had become "a catchall for all anti-transgender feminists, regardless of whether they are radical". Edie Miller, writing in "The Outline", said that the term was applied to "most people espousing trans-exclusionary politics that follow a particular 'TERF logic', regardless of their involvement with radical feminism". The term "TERFy" has also been used to describe things "that queer millennials deem uncool" such as bangs.
Opposition to the word.
Feminists described as "TERFs" generally object to the term and sometimes refer to themselves as "gender critical". British columnist Sarah Ditum wrote in 2017 that "the bar to being called a 'terf' is remarkably low." 
Some self-described gender critical feminists say they cannot accurately be described as trans-exclusionary because they say they are inclusive of trans men. Often, these feminists gender trans men as women. Writing for "Socialist Worker", American feminists Danelle Wylder and Corrie Westing say that this position is "divisive and contradictory" and that it represents "transmisogynist ideology".
In a 2015 article, American feminist scholar Bonnie J. Morris argued that "TERF" was initially a legitimate analytical term but quickly developed into a defamatory word associated with sexist insults. She described the word as "emblematic of the unresolved tensions between our LGBT community's L and T factions" and called on scholars and journalists to stop using it. 
British journalist Catherine Bennett has described the word as "a bullying tool" which has "already succeeded in repressing speech – and maybe even research".
British feminist author Claire Heuchan argues that the word is often used alongside "violent rhetoric". Heuchan adds that language of this type is used to "dehumanise women", often lesbians. British clinical psychologist and medical sociologist David Pilgrim argues that phrases like "Kill a TERF!" or "Punch a TERF!" are also posted by trolls online and there have been other depictions of violence aimed at women labeled as TERFs. 
The 2018 UK All Party Parliamentary Group (APPG) on Hate Crime received several submissions that indicated a high degree of tension between trans activists and feminist groups opposed to transgender rights legislation, with both sides detailing incidents of extreme or abusive language. The report noted that some women had submitted reports which argued that "women who object to the inclusion of trans women as female are being attacked both online and, in the street, with the term 'trans-exclusionary radical feminist' or (TERF) being used as a term of abuse."
Slur debate.
The people at whom the word "TERF" is directed often characterize it as a slur or hate speech. In a July 2018 solicitation of essays regarding "transgender identities", British magazine "The Economist" required writers to "avoid all slurs, including TERF", stating that the word is used to try to silence opinions and sometimes incite violence. 
Transgender rights activist and philosophy of language professor Rachel McKinnon has called the idea that the word is a slur "absurd", saying that just because a word can be used pejoratively towards women does not mean it is a slur in general. 
In August 2018, seven British philosophers wrote on the website "Daily Nous" that two articles by Rachel McKinnon and Jason Stanley published in the journal "Philosophy and Phenomenological Research" normalized the term. They described the term as "at worst a slur and at best derogatory", and argued that it had been used to denigrate those "who disagree with the dominant narrative on trans issues". In response, Ernest Sosa, the journal's editor in chief, stated that scholars consulted by the journal advised that the term could become a slur at some point, but that its use as a denigrating term in some contexts did not mean that it could not be used descriptively.
In a 2020 paper published in the philosophy journal "Grazer Philosophische Studien", linguists Christopher Davis and Elin McCready argue that three properties make a term a slur: It must be derogatory towards a particular group, it must be used to subordinate them within some structure of power relations, and the derogated group must be defined by an intrinsic property. Davis and McCready write that the term "TERF" satisfies the first condition, fails the third condition, and that the second condition is contentious, in that it depends on how each group sees itself in relation to the other group.
Author Andrea Long Chu describes the claim that "TERF" is a slur as "a grievance that would be beneath contempt if it weren't also true, in the sense that all bywords for bigots are intended to be defamatory."
Feminist philosopher Talia Mae Bettcher argues that, regardless of whether the term is accurately classified as a slur, it "has at least become offensive to those designated by the term", which suggests it might be best to avoid "in case one wants to have a conversation across deep difference".
Similar to describing "TERF" as a slur, some "gender critical" people also claim that the term "cis" is a slur.
The 2018 UK All-Party Parliamentary Group (APPG) on Hate Crime noted that, for threats of violence that included the term "TERF", "it would be difficult to successfully report this as hate speech as it is not completely clear if the abuse refers to lesbians ... or women" (if it referred to the former, it could be a hate crime).