it stands for involuntary celibates
An incel (a portmanteau of "involuntary celibate") is the name of a member --mostly white, male, and heterosexual-- of an online subculture who is unable to find a romantic partner despite wanting one. Known as "inceldom" they post messages in discussion groups describing their resentment, self-pity, self-loathing, misogyny, racism, a sense of entitlement to sex, as well as the endorsement of violence against sexually active people.
Historical perspective: The Southern Poverty Law Center described the subculture as part of the online male supremacist ecosystem that is included in their list of hate groups. As of 2018, there have been at least four mass murders, resulting in 45 deaths, committed in North America by people who have either self-identified as incels or who had mentioned incel-related names and writings on their social media postings.
See also : chat room bob  drump  lumpy  53X  
NetLingo Classification: Online Jargon