The Toronto van attack, which killed 10 people and injured many more, seemed like an unexplained and unexpected act of brutality. But it might have sprung from a horrifying and often neglected part of the internet.

Shortly before the attack on Monday, a chilling post appeared on the suspect's now-deleted Facebook feed. It saluted Elliot Rodger, and went onto use a number of words common to the dark internet community that appeared to have spawned it.

Calling Rodger "the Supreme Gentleman," the Facebook post declared: "The Incel Rebellion has already begun! We will overthrow all the Chads and Stacys!"

Toronto van attack: in pictures Show all 10 1 /10 Toronto van attack: in pictures Toronto van attack: in pictures The front end damage of the van that a driver used to hit several pedestrians in Toronto. AFP/Getty Toronto van attack: in pictures A lone police officer confronts the man suspected of driving the rented white van. rayy0889/Twitter/Screengrab Toronto van attack: in pictures Alek Minassian, 25, of Richmond Hill, a suburb north of Toronto, was arrested after he drove the vehicle into pedestrians. LinkedIn Toronto van attack: in pictures 10 people were killed in the city on Monday, 23rd April. AP Toronto van attack: in pictures Farzad Salehi consoles his wife, Mehrsa Marjani, who was at a nearby cafe and witnessed the aftermath. AP Toronto van attack: in pictures Emergency services closed Yonge Street after the van mounted a pavement crashing into a crowd of pedestrians. AP Toronto van attack: in pictures A covered body lies on Yonge Street. EPA Toronto van attack: in pictures Police inspect the van involved with the collision. Getty Toronto van attack: in pictures People sign a memorial for the victims. AP Toronto van attack: in pictures Police officers stand by a covered body. Aaron Vincent Elkaim/The Canadian Press via AP

It is not the first time that mass killings have focused attention on the community: it first came to prominence after the Isla Vista killings in 2014, when Rodger killed six people and then shot himself, leaving behind a manifesto that included rants about his hatred of women and his failure to get a girlfriend. Between the two events it has taken up an increasingly important part of life on the internet, with communities of people who identify with the name flourishing online.

Incel refers, in short, to "involuntary celibate" and is used in opposition to "volcel". People identifying with the name blame women for not having sex or relationships with them, and spend much of their time advocating against feminism and women more generally; at their most extreme, members of the group have suggested that men should be allowed to rape or physically attack women.

The rest of the words used in the Facebook post are characteristic of the group. The "Incel Rebellion" is a common idea that members of the group might rise up against a system they see as unfair to them. "Chads and Stacys" are words for popular and successful men and women – those who would not identify as incels.

While it rarely breaks into the mainstream the group of people calling themselves incels have taken root across much of the internet. Perhaps the most famous manifestation of the group was Reddit's r/incel forum, where people identifying with the name gathered largely to attack women and promote hateful rhetoric.

But it has spread its roots into darker parts of the internet, too. There are sites specifically devoted to discussing it, many of them full of misogynistic and hateful discussion, and it has also moved into infamous places like 4chan.

It was that sort of discussion that led Reddit to take down many of its most popular incel communities.

But it continues to host communities devoted to the group. It has a page known as IncelsWithoutHate, for instance, which exists "for all the people ... who don't feel the same hatred that is often expressed"; there is also a community called IncelTears that aims to find extreme views on Reddit and elsewhere and shut them down.

It is not clear the part the group in the attack in Toronto, apart from the post itself. (Facebook has confirmed the page and post belonged to suspect Alek Minassian, and has since shut it down.)

Toronto Police Services Detective Sargeant Graham Gibson told a news conference that those killed and injured were "predominantly" women, though he declined to discuss a possible motive.