The Brief: Incel stands for "involuntarily celibate" and refers to self-identifying individuals (usually heterosexual and male) who do not have sexual or romantic relationships, even though they want to.

DEEP DIVE
Incel stands for “involuntarily celibate” and refers to self-identifying individuals (usually heterosexual and male) who do not have sexual or romantic relationships, even though they want to.
The term comes from a now-banned Reddit and 4chan community in which sexually frustrated incels would commiserate about their situations.
Incel ideology is rooted in the idea that the women who reject incels (called Beckys and Stacys) and the men who date those women instead (called Chads) are to blame for their “involuntary celibacy.”
Although incels are not inherently violent, their attitudes are rooted in toxic masculinity.
Multiple acts of violence targeting women, including two mass murders, have been carried out by self-proclaimed incel assailants.
I may never stop thinking about the incels who believe they had a soulmate but she was aborted
— Brandy Jensen (@BrandyLJensen) July 12, 2018
The incels could just sleep with each other and it’d all be fine
— Joakim "konjak" Sandberg (@konjak) July 19, 2018