Over the weekend, thousands of people took part in Women's Marches to protest against sexism that pervades every aspect of society. But beneath the united front is a debate raging among activists about "terfs".

Terf is an acronym for "trans-exclusionary radical feminist", and is used to describe someone who doesn't accept that trans women are "real" women.

The row surrounding terfs erupted once again on Twitter after a marcher in Vancouver was photographed holding a sign reading "Trans women are men. Truth is not hate. Don't believe the hype.

The sign added: "Trans ideology is misogyny and homophobic. Woman is not a 'feeling', a costume, or a performance of a stereotype. Woman is a biological reality. There is no ethical or moral duty to lie to soothe a male ego."

Peppermint, a former contestant of RuPaul's Drag Race and an open trans woman, was among those to call out the protester. She wrote on Twitter: "I disagree with this woman. I imagine many who agree w/ her would ALSO deny her right to: choose, Vote, equal pay & marriage equality. Women should'nt be defined or confined by ANYONE including men, trans-women should'nt be defined or confined by ANYONE especially cis-women."

Others online accused the protester of being a terf and transphobic. We unpack the origins and connotations of the term below.

Where does the word come from?

A blogger named Tigtog is believed to have coined the word in a 2008 post distinguishing feminists who believe that trans women qualify as women and those who don't, according to the New Statesman.

"Terf" itself is controversial and regarded by some as a slur, while others view it as neutral definition of a set of beliefs. It is unusual, however, for someone to call themselves a terf.

Similarly, few would call themselves a racist, although their beliefs and actions might align with the accepted definition of the word.

What are people arguing about?

It is widely accepted that sex is the classification of a person as male or female according to their anatomy. This is generally assigned to a person by a clinician at birth who assesses a baby's genitals. For instance, a baby with a penis being regarded as a boy.

Gender, on the other hand, describes how someone feels based on their personal sense of how society's ideas of masculinity and femininity relate to them. "Man" and "woman" are therefore both gender identities. Cis-gender defines a person whose sex and gender expression match up, for example a person with a penis feeling they are a man. Most people assume that a person with a penis will grow up to be a man, but this isn't always the case.

A person might describe themselves as trans if their gender expression doesn't match up with the gender they were assigned at birth. For instance, someone with a penis who identifies as a woman.

Women's march sign
A sign at the LA Women's March reads 'all bodies are beautiful'. Chelsea Guglielmino/Getty Images

The debate comes down to a theory called biological essentialism. In the context of gender, this belief centres around the idea that a person being a man or a woman entirely comes down to an innate, "natural" essence, rather than as a product of their culture.

They might believe that trans women or trans men are not "truly" women or men because of their anatomy. However, the argument is largely focused around trans women. This comes down to the unique experiences they believe that cis-gender women have growing up and dealing with sexism and inequality.

This stands in opposition to intersectional feminism, where the rights of oppressed groups are considered in relation to one another in the fight for rights and equality.

For instance, white women recognising their privilege in relation to women of colour and working together rather than in opposition. This type of feminism recognises that trans women also experience hardship similarly to cisgender women, because of the patriarchal structures of society. It is also seen as reductive to believe that all women share the same experiences that somehow qualify them as "real women".

Someone who doesn't accept a trans woman as a "real" woman might argue that they don't understand what it is like to have their first period and the stigma which surrounds it. However, this argument ignores the fact that some cisgender women may not have a period for medical reasons, but they would still be considered women.

Activists are concerned that these beliefs will further marginalise trans people as they fight for equal rights.

Who has been called a terf?

Academic and influential second-wave feminist Germaine Greer was accused of being terf after she told The Guardian: "Being a woman is a bit tricky. If you didn't find your pants full of blood when you were 13 there's something important about being a woman you don't know. It's not all cake and jam."

BBC Women's Hour Jenni Murray was also labelled a terf after she wrote a piece in The Sunday Times Magazine titled "Be trans, be proud - but don't call yourself a 'real woman'."

Writer Chimamanda Ngozi Adichie was similarly criticised for saying that "trans women are trans women" when asked if they are women.

Seminal feminist Gloria Steinem also expressed her belief that trans women are not women. However, she later changed her mind and wrote in The Advocate:

So now I want to be unequivocal in my words: I believe that transgender people, including those who have transitioned, are living out real, authentic lives.

Those lives should be celebrated, not questioned. Their health care decisions should be theirs and theirs alone to make. And what I wrote decades ago does not reflect what we know today as we move away from only the binary boxes of "masculine" or "feminine" and begin to live along the full human continuum of identity and expression.

This article was originally published on 24 January.