A crowd gathers for a huge 15-county job fair in Ringgold, Ga., in April (Dan Henry/Associated Press)

Among the economic and social trends worth worrying about is the fate of the NEETs. Never heard of the NEETs? I hadn’t either. It’s one of those clumsy terms concocted by government bureaucrats and social scientists to designate a group, social condition or political problem — and then to make it obscure by wrapping it in jargon. NEETs refer to young people who are “neither employed nor in education or training.” There are roughly 39 million NEETs in 33 of the world’s advanced industrial countries, according to a new report from the Organisation for Economic Co-operation and Development (OECD).

I have written before about the problems of U.S. millennials — young adults born after 1980. They are the victims of poor timing and indifferent public policies. Coming of age in a harsh economy, they find it hard to get work (especially work for which they’re qualified). By the millions, they’re living with parents and postponing marriage, children and home-buying. Many are burdened with heavy student loans. Those with jobs subsidize their usually better-off elders through Social Security and Medicare payroll taxes.

Let me repeat what I’ve said previously. Treat generational generalizations skeptically. Many millennials are doing fine; others would struggle in the best of times. Still, their collective prospect is “substantially worse than that of [recent] generations of Americans” through no fault of their own, as Diana Furchtgott-Roth and Jared Meyer write in “Disinherited,” their book on millennials.

The NEETs are a similar phenomenon on a global scale. In each of Britain, France and the United States, NEETs were 16 percent of the 15-to-29-year-old population in 2013, reports the OECD. In South Korea and Ireland, their share was 19 percent; in Italy, Spain and Greece it was slightly more than 25 percent. As disturbing, a quarter of those with jobs had temporary work.

Granted, young adulthood is a time of life when, in rich societies, people search for the right job, the right living place, the right mate. There’s more changing jobs, moving around and idleness. Even so, the pool of disengaged youth now seems bloated, posing two obvious questions.

The first is whether — or how much — their extended joblessness will inflict permanent damage on their future employability and earnings. A job is not just a paycheck. It’s also an education. Some skills are simple but crucial: showing up on time; learning how to take instruction; dealing with customers or co-workers. Other skills involve specialized competencies that, as often as not, are taught or perfected on the job and not in school.

The longer workers don’t get these skills, the harder it becomes to succeed in the job market. They don’t develop the personal contacts that help them find and keep work. They’re less appealing to businesses. They become stigmatized. Employers wonder why they’ve been without a job for so long.

The second question is more profound. Does prolonged unemployment (and, perhaps, dependence on parents) erode their confidence, undermine their ability to form durable relationships and radicalize their politics? Being outside the economic mainstream could become a semi-permanent condition that exerts a pervasive influence on their beliefs and behavior. They might live on the fringes of society.

They could become a “burden for their countries . . . from lower tax revenues, higher welfare payments, and the social instability that may arise when part of the population is out of work and demoralised,” warns the OECD.

To be sure, there are correctives. Jobs are paramount. Older workers will retire or die, opening up permanent slots for the young. The plodding global economic recovery may slowly reduce the ranks of the jobless. In the United States, lower unemployment has already helped.

Another possibility: Advances in digital job services (the next Monster.coms and LinkedIns) may make it easier for qualified workers to find rewarding employment. Just last week, the McKinsey Global Institute — the research arm of the well-known consulting company — issued a study predicting that new matching technologies “could shorten search times between jobs, reducing the duration of unemployment.”

Is this wishful thinking?

What we know for certain is that many countries — rich and poor — have a stubborn glut of unemployed youth. By the OECD’s estimates, roughly half of the NEETs aren’t even looking for work. That is a somber warning sign of political and personal fatalism. The 20s are too early in life for people to have abandoned hope. One test for many advanced democracies is whether, for this group, they can promote a sense of purposefulness and self-reliance.