FOMO is a worried, restless feeling you get when you think other people are having more fun than you, or living a more exciting life than you. You picture the party you skipped, the trip you did not take, the photos everyone else is posting — and you feel left out. It is informal, and it belongs especially to phones and social media, though people now use it for ordinary life too: missing a sale, a class reunion, even a new restaurant. Younger speakers say it a lot; it still sounds a bit trendy in a formal meeting. People also stretch it. They say ‘I have FOMO’ for a light wish, not only for real anxiety. Some even use it as a verb: ‘I FOMO’d and bought a ticket.’ That verb use is very casual. The feeling is old; only the name is new.