One of the most prominent think tanks in the US has officially determined what makes a millennial a millennial.

Or at least, they have determined the age range that forms the generation, which has intrigued researchers but defied definition for years.

Pew Research Centre announced this week that they would be applying the term “millennial” only to those people born between 1981 and 1996. That means all millennials – at least according to Pew – will be between the ages of 22 and 36 in 2018.

“In order to keep the Millennial generation analytically meaningful, and to begin looking at what might be unique about the next cohort, Pew Research Centre will use 1996 as the last birth year for Millennials for our future work,” Pew Research President Michael Dimock wrote in a blog post.

The definition of the term “millennial” is an elusive one, which many use simply to describe young adults in general. But Mr Dimock said his team was able to determine a few characteristics that set millennials apart, making it possible to set a firm age range.

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First, American millennials grew up in an era defined by the September 11 terrorist attacks. Most of them were old enough to grasp the severity of the event when it occurred, and still remember it now. They then came of age during the wars in Afghanistan and Iraq, and the intense political polarisation those helped usher in.

Millennials were also between the ages of 13 and 27 when the first black president was elected in the US – largely on the strength of the youth vote. They also came into adulthood in the midst of the ensuing recession, which shaped many of their career trajectories for years to come.

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Finally, according to Pew, millennials can be distinguished from the generations before and after them for their relationship to the internet. Most millennials came of age as the internet became ubiquitous, and were rapid adopters of the new technology – to the chagrin of many in the older generation.

But members of the generation below them – sometimes referred to as Generation Z – never knew a time without such technology. Millennials had to adapt to social media and constant connectivity, Mr Dimock wrote, while post-millennials take them as a given.

The new definition leaves open the question of what to call the generation after the millennials – what Pew is calling the “post-millennials” for the time being. When the New York Times asked the generation to name themselves, they got suggestions ranging from “the Meme Generation” to “The Cleaner-Uppers”.

Some, however, said they preferred not to be labelled at all.