Alek Minassian drove a rented van into a crowd of people in Toronto, Canada, Monday—killing 10 and injuring 14. The 25-year-old was arrested and charged Tuesday with 10 counts of first-degree murder and 13 counts of attempted murder. According to reports, another count of attempted murder likely will be added. Minassian’s motive is unclear, although a message he posted to Facebook—which has now been removed—before the attack could offer some insight.

“The Incel Rebellion has already begun! We will overthrow all the Chads and Stacys! All hail the Supreme Gentleman Elliot Rodger!” part of the message read.

Incel: a little-known word that—in the last 48 hours—has become a trending topic.

Incel is short for “involuntarily celibate,” a term that and was originally coined in 1993 by a queer woman searching for a way to describe her sense of loneliness, and to connect with others who felt the same. The phrase has since been co-opted by an online community of men who are, in the simplest terms, angry that they can’t convince women to have sex with them. Unlike typical men who are irked they’re not having sex, incels don’t grouse to their friends over beers and try to pick up girls at bars—they talk about overthrowing feminism and, often, plot violence against women including advocating for state-sanctioned rape on subreddits like r/braincels, on 4Chan, and on various sites like incels.me.

“A lot of [these guys] are pretty young, and I think some of it stems from standard adolescent insecurities and sexual frustration and anger at being rejected by girls,” says David Futrelle, a writer and creator of We Hunted the Mammoth, a blog that examines the new wave of misogynists bred by the internet. “But instead of growing out of this, they turn it into a lifestyle.” Futrelle says other men who identify as incels could be dealing with serious issues like depression and social anxiety—but instead of trying to get those treated with therapy or meds, they blame the alleged cruelty of girls and women for their woes.

Like most tightly-knit online communities, incels have developed their own language; a shorthand for describing the men and women they loathe, as evidenced by the mention of “Chads” and “Stacys” in Minassian’s Facebook post.

“Chad is the stereotypical asshole hunk who gets all the girls—think of the jocks from Revenge of the Nerds or the guy who kicks sand on the skinny guy in those old Charles Atlas ads,” says Futrelle. “Stacy is the Barbie to Chad’s Ken, the stereotypical hottie who will never give an incel a second glance, and who apparently spends most of her time riding what [incels] call the ‘cock carousel’ with every Chad they can get their hands on. According to Futrelle, many incels think that Chads are the only men who ever have sex with women.

“This all may seem a bit ridiculous, but it’s no exaggeration,” he says. “This is how they think. I’m convinced that they literally visualize Chads as characters in ‘80s teen flicks.”

Benchmarks of an incel can include feelings of entitlement and resentfulness, with many feeling like sex is something that’s owed to them. “Some have even demanded that the government provide them with girlfriends and/or prostitutes,” says Futrelle.

Logic would dictate that these men have been consistently trying to find women to have sex with, but Futurelle says that’s not always the case.

“[Many] don’t know how and think it’s pointless. Incels hate women but they also hate themselves, and many of them convince themselves they’re too ugly or too short to ever be attractive to women, he says. “Of course when they post pics of themselves for other incels to judge they tend to be perfectly ordinary looking people; their ugliness is all in their head.”

Relationships expert Hunt Ethridge, who has followed the incel movement since its inception and has had some its disciples as clients, likens incels to the fox in Aesop’s fable – the fox couldn’t reach the grapes he wanted, so he convinced himself the grapes were sour and he didn’t want them anyway.

“It’s a psychological ploy,” he says. “You can’t go through life thinking you’re bad, so you find a way to decide you’re the victim.”

He explains that many incels are extreme narcissists who see themselves as superior in every way to other men, and that when they see men who they consider inferior to themselves (“Chads”) getting access to the “resource” (aka women) that they can’t attain themselves, they get angry. They feel wronged and cheated, and think that women are making a mistake by passing up their obviously superior offerings.

“A lot of these incels come from the bad version of the ‘nice guy’ mentality,” Ethridge says, “where they feel like it’s transactional, they feel like they’ve given so much by being nice guys and gotten nothing in return. Even though that’s not how it works.”

Incels were in the news in 2014 after 22-year-old self-identified incel Elliot Rodger killed six people and then himself in Isla Vista, California. Before his rampage, Rodger wrote a “manifesto” and posted online frequently about his hatred of women and his outrage at the fact that they didn’t want to have sex with him (apparently not realizing the contradiction of those two sentiments). In one post he wrote, “One day incels will realize their true strength and numbers, and will overthrow this oppressive feminist system. Start envisioning a world where WOMEN FEAR YOU.”

There’s always been angry men but, during the last decade or so, the internet has given them a permanent home; a makeshift family of male sympathizers who have built an entire online ecosystem from their rage. This is known as the Manosphere, an array of misogynistic groups and sites. “One of the central beliefs is that feminism has given women too much power— in the workplace, in politics, in the bedroom—and needs to be destroyed,” says Futrelle. “But the vast majority of’Manosphere’ men not only hate feminism; they hate women, and blame them for virtually everything they don’t like.”

“Frustrated men who feel that they don’t have access to resources have been the start of all worldwide rebellions,” Ethridge adds. “These guys see themselves as revolutionaries. And it’s really scary, because a lot of them don’t have anything to lose.”

Minassian posted on Facebook moments before the deadly van attack this week praising Rodger, who has frequently been referred to in incel circles as “Saint Elliot.” This widespread praise was one of several points raised in a petition to shutter the r/Incels subreddit, which had around 40,000 members before Reddit shut it down in 2017.

Still, shutting down one of their online hubs didn’t shut down the “movement.” They still gather on various corners of the web, like the message board incel.me where one user posted about the Toronto killer shortly after Monday’s attack, writing, “I hope this guy wrote a manifesto because he could be our next new saint.”

“An argument for why Reddit shouldn’t have shut down the incels group is because of what happens when you turn the light on in a room full of cockroaches—they scatter,” Ethridge says.

Independent online harassment researcher Caroline Sinders, whose interest in the darkest corners of the internet started with Gamergate, is in favor of shutting down incel’s subreddits and message boards completely before they produce more violent actions like Rodgers’ and Minassian’s. (A statement from Reddit following the ban on the incel subreddit in 2017 said the move was in line with an earlier policy to ban content that calls for violence or physical harm, including forums for Nazi, racist and white supremacist groups.)

“Allowing that kind of behavior to proliferate is problematic, it allows for problematic content and norms to flourish, it does create a gray area not just of ‘words’ but of actions.”

In other words, if these message boards go unchecked or are written off as harmless venting or joking, they actually pave the way for incels to encourage each other to take their dangerous, misogynistic views beyond the Manosphere and into the real world where, as we’ve seen with Rodgers’ and Minassian, they pose a very real threat.