As a new notion takes root in the zeitgeist one can find competing definitions circulating in popular culture and scholarly literature. This is especially so for what linguist Donna Gibbs (2006lc, p. 30) called cyberlanguage, with "its own brand of quirky logic, which evolves with unprecedented speed and variety and is heavily dependent on ingenuity and humor." One can see this evolution play out at Urban Dictionary (UD), a Web repository for (over eight million) definitions of contemporary popular culture, slang, and Internet memes. Submissions, which include a definition and optional examples of usage, can be made by anyone providing an email address; other contributors then vote upon whether a definition ought to be accepted. (One word can have multiple definitions; the term "Urban Dictionary" entry has hundreds (Lucy2005ud).) UD's earliest definition of FOMO as a type of fear is from 2005 and it simply expands the acronym and provides an example phrase "Jonny got the rep for being a fomo, but jake's a bigger one" (Justinas2005fmo). This example phrase is odd in that it is something one is rather than something one feels; in this, it is much closer to an older meaning of FOMO as a "fake homosexual." In any case, a better definition (and the most popular one) was posted in 2006: "The fear that if you miss a party or event you will miss out on something great" (Beaqon2006fmo). This definition and point in time marks the ascendancy of FOMO in popular culture: many more definitions would appear at UD and elsewhere in the following years.
Beyond penning definitions, lexicographers also attempt to find the origins and early exemplars of a term. For instance, the august Oxford Dictionary (2014fmo) locates FOMO's origins in the "early 21st century." While there's no evidence of single point of origin, I think we can be more precise than that. FOMO's usage, unsurprisingly, coincides with the launching of Facebook in 2004 and Twitter in 2006. For instance, Kathy Sierra, a popular tech blogger, wrote how Twitter fueled the fear in the year after its launch.
Ironically, services like Twitter are simultaneously leaving some people with a feeling of not being connected, by feeding the fear of not being in the loop. By elevating the importance of being "constantly updated," it amplifies the feeling of missing something if you're not checking Twitter (or Twittering) with enough frequency. (Sierra2007cpu)
(Apparently, at this point "tweeting" had not yet eclipsed "twittering.") In the same year, Lucy Jo Palladino (2007fyf) dedicated a section of her book on how to "defeat distraction and overload" to FOMO, though she focused on examples beyond social media, such as parents' anxiety that their children are falling behind. The earliest mention of the term on Usenet (the pre-Web fora of the Internet, which still muddles along) appears to be from 2008 (Bewdley2008hyg). By 2010, FOMO was being used and spoken of broadly and unambiguously tied to social media usage. By 2011, the phenomenon was something that others recognized they could take advantage of. A marketing report from JWT Intelligence ("converting cultural shifts into opportunities") recommended that "brands can focus on easing it, escalating it, making light of it or even turning it into a positive" (Miranda2011fm, p. 5, 17). Capping its seven year ascent, the notion was recognized by the Oxford dictionaries (OxfordWords2012bwa) as the "Anxiety that an exciting or interesting event may currently be happening elsewhere, often aroused by posts seen on a social media website."
In 2013, FOMO received its first scholarly attention from social psychologist Andrew Przybylskia (2013meb, p. 841) and his colleagues. They defined it as "a pervasive apprehension that others might be having rewarding experiences from which one is absent, FOMO is characterized by the desire to stay continually connected with what others are doing." In this definition we see a recognition of an emotion (i.e., anxiety) and a characteristic behavior. Similarly, contemporary discussion of FOMO invokes multiple, often tangled, references to varied emotions (e.g., anxiety) and behaviors (e.g., compulsive checking). Hence, it is worthwhile to further understand what it is that people are speaking of when the lament a fear of missing out.