When you find yourself mansplaining the term “mansplaining” to a worked-up faction of Twitter on a Sunday evening, you can assume you’re not getting the best out of your leisure time. And that’s not even the most foolish thing a man called Paul Bullen did over the weekend.

On Saturday, the Guardian published an extract from an upcoming book, Womanhood: The Bare Reality by the photographer and writer Laura Dodsworth. Alongside photographs of external genitalia was first-person testimony from the subjects pictured. Titled “Me and my vulva: 100 women reveal all”, it was an arresting story. Bullen spotted the article on Sunday, and responded with a tweet that he probably (well, hopefully) now regrets: “The correct word is vagina.”

Until I wrote a book about vaginas and vulvas, I called my own vulva a vagina

Suddenly, social media was abuzz with vulva and vagina chat as women came forward to chastise Bullen for his mistake. Gleefully, they rushed to let him know that the vagina is the muscular tube that connects the vaginal opening to the cervix – whereas the vulva is the external genitalia, including the labia, the clitoris and the vaginal and urethral openings. It is then that a more sensible man might have logged off or even deleted his tweet, but Paul Bullen didn’t give up. In fact, he got into a separate argument about the definition of “mansplaining” and then doubled down on his vagina/vulva assertion.

“I am supporting widespread female usage, as in The Vagina Monologues,” he argued. “I am defending how actual people speak.”

It is here, I must concede, that Bullen has a point. The word vagina is regularly misused. In fact, until I wrote a book about vaginas and vulvas, I called my own vulva a vagina. I knew that I was supposed to call it a vulva but I thought that the word “vulva” sounded a bit stuffy, a bit pedantic. Given the dearth of words women have to describe their genitals (“pussy” is too porny; “cunt” is too sweary; “front bottom” is just ridiculous), most of us have relied on “vagina”, even if it isn’t anatomically correct.

However, when I began to write extensively about female health and sexuality, I realised that by not using the word vulva, I was doing myself and my genitals a disservice.

The American feminist and psychologist Harriet Lerner believes that neglecting the word vulva has serious consequences, calling it a “psychic genital mutilation”. “What is not named does not exist,” she argues. The vagina is essential for heterosexual penis-in-vagina sex and childbirth and so the word has come to be tolerated if not exactly celebrated. The vulva – with its clitoris – represents something more taboo than even sex and menstruation: female pleasure. It is a place of independent female sexuality, a place that can exist – happily – unperturbed by a penis. And so the vulva has been sidelined.

Suddenly, though, more and more of us are keen to say, see and celebrate vulvas. As well as Dodsworth’s project, there’s a book forthcoming from The Vulva Gallery, a website and Instagram account featuring hundreds of illustrated vulvas by the Dutch artist Hilde Atalanta. Both Dodsworth and Atalanta have spoken about how an ignorance of basic biology has serious ramifications for people – in terms of pleasure, confidence and gender equality. And as women recognise the lack of information they’ve been given about their own bodies and the consequences that has had – particularly in the wake of the #MeToo movement – there is an increased focus on our biology and the language we use to describe it.

Using the words vulva and vagina interchangeably isn’t a harmless linguistic quirk: it’s actually a technique for diminishing a woman’s sexual agency. Anyone who cares about language – and women – should recognise that.

• Lynn Enright is a journalist and the author of Vagina: A Re-education, published in March 2019