Among generations, boomers are easy to identify, and millennials have made their mark.

But who is a Xennial and where did Gen Alpha come from? And Generation Jones?

The contemporary naming of generations dates back to poet Gertrude Stein, who wrote of those who came of age during World War I, “You are all a lost generation.”

Nearly a century later, names, labels and character studies for the generations have multiplied.

By the numbers

Baby Boomers: born 1946 to 1964

The baby boomer generation — the only generation officially recognized by the U.S. Census Bureau — began immediately after World War II (with people born in 1946) and wrapped up in 1964. These days, boomers are in their late 50s to early 70s, many about to be or already retired.

Generation Jones: born 1955 to 1965

Younger boomers — titled Generation Jones to reflect “keeping up with the Joneses” culture, the slang term “jones” for desire, the confusion of Bob Dylan’s Mr. Jones, and just the generic anonymity of the Jones name — were born between 1955 and 1965.

Generation X: born 1965 to 1980

With a decline in birth rates in 1965 came Generation X, which demographers generally say lasted until 1980. Gen X is also called the “baby bust” because of its smaller post-boom numbers.

Xennials: born 1977 to 1983

Squeezed in next was a “micro-generation” of Xennials born in the late ’70s and early ’80s. Also known as the “Oregon Trail generation,” Xennials had an analog childhood and a digital adulthood.

Millennials: born 1981 to 1996

According to Pew Research Center, Millennials were born between 1981 and 1996. The older segment of the demographic are well into adulthood. Millennials are also called Generation Y for following Generation X, and as the children of boomers, they’re sometimes called “echo boomers.”

Generation Z: born 1997 or after

Then came Gen Z, or iGen, which roughly starts with people born in 1997.

Generation Alpha: born 2010 or after

What comes after Gen Z? Some researchers are using the name Generation Alpha for kids born since 2010. We’ll see if that catches on in the coming years.

Many observers debate the precise dates and definitions or decry stereotypes attached to each generation. Nevertheless, their shared values and experiences shape education techniques, marketing strategies, purchasing decisions, work styles, voting preferences, social service needs, entertainment choices, musical tastes, and more.

Technology by the numbers

One of the biggest experiences shared by a generation is the technology it grew up with.

Boomers passed through childhood as television took hold, Generation X saw computers come onto the scene and millennials were born into the age of the Internet.

More recently, members of iGen or Generation Z are the first to grow up with smartphones, said Dr. Jean Twenge in her book  iGen: Why Today’s Super-Connected Kids Are Growing Up Less Rebellious, More Tolerant, Less Happy — and Completely Unprepared for Adulthood — and What That Means for the Rest of Us.

Absorbed with social media and texting, they are said to spend less time with their friends in person, which could be making them anxious or lonely, experts like Twenge say.

What defines a generation

Older Baby Boomers observed the Korean and Vietnam wars, and older members of that generation also participated in the latter.

Generation Jones had Watergate, the 1979 oil embargo, and AIDS, fostering what many see as a loss of trust in government and other institutions.

Those in Generation X are “the last Americans that know how to fold a newspaper, take a joke, and listen to a dirty story without losing their minds,” Vanity Fair magazine once wrote.

But Gen Xers also are described as the first “latchkey” kids, exposed to daycare and divorce that made them cautious and pragmatic.

During a short grace period, Xennials went to school before Columbine and found jobs before the recession.

Millennials learned about popular culture via cable television, joined the workforce at the height of the recession and delayed leaving home and marriage, giving them a “slow-start” reputation. They were old enough to understand the Sept. 11 attacks, helped elect the nation’s first black president and are the second-largest generation of voters after baby boomers

Generation Z will have more money than any previous generation — but more school debt as well. Donald Trump may be the first U.S. president they know.

But does it really matter?

Not everyone buys into the concept of generations, by the way.

A Slate magazine piece argued there was no scientific evidence to support the distinct characteristics of generations and that the concepts were arbitrary, flawed and stereotyped.

“Generations and generational differences are intriguing and inherently appealing concepts. As such, the media will keep on reporting on them, academics will publish, pundits will talk, and consultants will sell to whoever is buying,” it said.

“But the science says that, despite their popularity, generations simply aren’t a thing.”