n. The fear of missing out on something interesting or fun, particularly when it leads to obsessive socializing or social networking.
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It begins with a pang of envy. Next comes the anxiety, the self-doubt, the gnawing sense of inadequacy. Finally, those feelings fizzle, leaving you full of bilious irritation.

Whether it's triggered by Laura's tweet from backstage at that gig or Joe's photos from his tropical retreat, most habitual users of social media will recognise the syndrome, which now has an equally irksome acronym: Fomo.

For the uninitiated, that's "fear of missing out"
—Hephzibah Anderson, “Never heard of Fomo? You're so missing out,” The Guardian, April 17, 2011
The patrons — 30 per seating, two seatings per night — enjoy cuisine from a rotating roster of local star chefs. The buzz about the venture has been almost rabid, with passionate bloggers speculating on the identity of each surprise chef (the first was Marc Cassel from Park), leading to sellouts. It's all for a good cause, as each seating is expected to raise about $500 for a group of local charities.

48 Nights' organizers clearly have the followers, which draws the coveted chatter. Add in an expiration date and the potential FOMO — fear of missing out — only escalates the notion of exclusivity.
—Jason Sheeler, “Temporary shops, galleries, eateries popping up in Dallas,” The Dallas Morning News, March 02, 2010
It's a great event; I feel like I have to go, since it's free for me. The real reason is this thing called FOMO; it's a disease, the Fear Of Missing Out syndrome," says Acacia. "She has to go to every festival," adds Erin, "and now she has me coming along.
—“Why Reggae?,” North Coast Journal, August 12, 2004
2004 (earliest)
Why would so few people respond to an invitation for a birthday party at Trio, especially when it’s been sent to 350 close friends? The answer is simple. It all comes down to what I’ll call McGinnis’ Two FOs: FOMO and FOBO. Allow me to explain.

First year, especially first semester can be a trying time socially. In this state of social flux, FOMO, or Fear Of Missing Out, weighs heavily on the psyche.
—Patrick McGinnis, The Harbus, May 10, 2004
FOMO was recently nominated for both Word of the Year and Most Useful word by the American Dialect Society.