Short for involuntary celibate, meaning the inability to get a date/intimate female attention.
Incel's can be otherwise very normal people with normal mental, emotional, and physical states. However, ask any incel and he (most times a male) will tell you the thing he wants most in the world is a meaningful relationship, sex aside. Ironically, women have little romantic interest, and will friendzone the incel, causing emotional trauma and can lead to love shyness.
These people are often polite, intelligent, and even funny around their friends (which can include women). In addition, they are spiritual, and have well defined identities from trying to fix themselves for the opposite sex. Nevertheless, they are doomed to be alone because of minor flaws in character, interests, or physical appearance.
Imagine being the only kid on the playground without a new toy everyone takes for granted. You are allowed to see and touch the toy, but can never play with it or have your own. When the toy breaks, they ask you to fix it then take it right back. That's what it feels like to be an incel.
involuntary celibate: someone who is celibate but doesn't want to be
"He's an incel. He tries to get dates every week but gets turned down all that time."