Fun fact: The University of California-Los Angeles (UCLA) has produced a slang dictionary every four years since 1989. Within it are over 1,000 entries defining words and phrases the kids use these days around Westwood campus. “Sister from another mister,” “bromance,” “eargasm,” as well as popular abbreviations such as IDK (“I don’t know”), are but a few examples of what’s been included.

As hard as it is to reconcile, these terms aren't just the jargon reserved for millenials. Some of today’s pop culture concepts and phrases have real, science-backed meaning. We’ve rounded up a handful of examples for you to check out below.

FOMO

Arguably the most used abbreviation today, FOMO refers to someone with a “fear of missing out.” Boston Magazine reported the first paper on FOMO surfaced in the year 2000 while the first “chronic outbreak” occurred at Harvard Business School in 2004. And an Oxford University study found FOMO can mean general discontent — something today’s constantly plugged-in culture exacerbates. In fact, according to a Mashable survey, 56 percent of people are afraid of missing out on events, news, and important status updates.

FOMO seems like it’s something said in jest, perhaps after your co-workers all venture to trivia night on a night you’re unavailable, but it has a very real, psychological effect. A study published in the Annals of the New York Academy of Sciences found FOMO can lead to feelings of anxiety and depression. There are separate studies that suggest FOMO has the opposite effect, that it can encourage people to be more social. Regardless, both can agree FOMO is for real.

Hanger

Hunger plus anger equals hanger. Someone could alternatively say, “I’m hangry,” and it would still mean they’re likely to turn into a monster without food, and soon. It’s not this made-up concept people use to excuse their aggressive eating behavior; it’s an effect of low blood sugar. A study published in the Proceedings of the National Academy of Sciences measured glucose levels in 107 married couples over three weeks. They found the lower a participant’s blood sugar, the more they took it out on their partner.

Why you gotta be so rude, hangry people? Study researchers explained energy is required in order to self-control those aggressive impulses, and this energy comes from the food we eat. Running on empty can also trigger brain, stress, and the shakes. Dr. Sue Decotiis, an appetite specialist, told Refinery 29 those who skip breakfast, and those who eat too much sugar, simple carbs, and processed foods are more prone to hanger.

Selfie

A photographer in 1839 is credited with taking the first-ever selfie (the act of a person holding their phone out in order to take a picture of themselves, probably inspiring a severe eye roll). So we’d be curious to know how that photographer would feel upon hearing the negative impact selfies have had on the population, from the inception (and rise) of “selfie surgery” to decreased self-esteem.

Instagram, Photoshop, and otherwise photo-editing apps make it easy for men and women to filter flaws out of their photos. Even when a person knows an Instagram picture isn’t an accurate portrayal of the person in real life, it still makes them feel bad about themselves. A recent Glamour survey found the longer women spend time online, the worse they feel about themselves. Selfies are now a gateway into poor body image. According to psychiatrist Dr David Veal, “Two out of three of all the patients who come to see me with Body Dysmorphic Disorder since the rise of camera phones have a compulsion to repeatedly take and post selfies on social media sites.”

Thin-, Fat- And Slut-Shaming

We lumped these three together because shame is the quintessential emotion rooted in low self-esteem and family dysfunction. “Early in life, individuals develop an internalized view of themselves as adequate or inadequate within the world,” Dr. Marilyn J. Sorensen, Ph.D., author of Breaking the Chain of Low Self-Esteem, told Psych Central. “Children who are continually criticized, severely punished, neglected, abandoned, or in other ways abused or mistreated get the message that they do not ‘fit’ in the world — that they are inadequate, inferior or unworthy.”

Thin-shaming may be less ubiquitous than fat- or slut-shaming, but it’s garnering a very genuine debate on its equally harmful effects. Hannah McGoldrick, an associate editor for Runner’s World, bravely opened up about her personal battle with anorexia after commenters said she looked as much, the point being shame can carry so much more weight for some people. Whether a person feels shame for being “too fat,” “too thin,” or too “sex positive,” it then has the potential to lead to destructive behaviors.

Resting Bitch Face

Urban Dictionary defines RBF (also known as “bitchy resting face” and “chronic bitch face”) as “a person, usually a girl, who naturally looks mean when her face is expressionless, without meaning to,” thus the resting part. To science, this is known as “face-ism” — and it prompts people to judge another person’s trustworthiness, competence, extroversion, and dominance before they’ve opened their mouth to talk. “One we see a person's face, we put so much weight on that cue that we end up ignoring other, more useful pieces of information,” Christopher Olivola, who researches the psychology of human decision making at Carnegie Mellon University, told TODAY.

Short of getting a grin lift — procedure that turns a mouth upward to give off a happier expression — making an effort to smile more can discourage another person’s snap judgements.