They are considered less cynical and pessimistic than Gen X, variously defined as being born from the mid 1960s to early 1980s, but not as optimistic or entitled as Gen Y, born from the early 1980s to late 1990s.
The term is a solution to recent complaints by "Old Millennials" that they don't feel as though they fit the avocado-eating, Snapchat-loving mould of the endlessly dissected generation - but also don't really remember the first Star Wars movies.
Every generational shift tends to create a "swing" section, or micro-demographic on the cusp, that doesn't quite fit with the previous or next cohort. But experts believe the sense of isolation is particularly relevant for the X-Y in-betweeners.
That's mainly down to technology, which has totally disrupted our lives and changed how we experience the world in hugely significant ways. If you grew up with high-speed internet and social media, it's likely to have shaped you in unprecedented ways.
In 2014, Good.is wrote about these "generational misfits" for whom September 11 was formative, who didn't know about sexting, but didn't really get grunge, "born somewhere in between Halloween and A Nightmare on Elm Street."
via GIPHY
A year later, Social Media Week examined the people who remember the agonising wait for dial-up connection, asking A/S/L (age/sex/location) in chat rooms and got safely through university without the embarrassment of social media.
That was the same year Juliet Lapidos wrote a New York Times column entitled Wait, What, I'm a Millennial? "I don't identify with the kids that Time magazine described as technology-addled narcissists, the Justin Bieber fans who 'boomerang' back home instead of growing up," she said.
In April, New York Magazine discussed the phenomenon of "Old Millenials" born before 1988, who act as a different "self-contained generation" largely because of two epochal events - the smarphone takeover and the financial crisis. Many of this demographic were in the workforce, or just sneaking in, so the GFC didn't effect their job hunt too much. On the other hand, they typically weren't on the property ladder yet, like most Gen X-ers.
They've been called the Oregon Trail Generation (after a computer game), the Lucky Ones and Generation Catalano, after Jared Leto's character Jordan Catalano from My So-Called Life.
Dan Woodman, associate professor of Sociology at the University of Melbourne, told Mamamia: "The idea is there's this micro or in-between generation between the Gen X group - who we think of as the depressed flannelette-shirt-wearing, grunge-listening children that came after the Baby Boomers and the Millennials - who get described as optimistic, tech savvy and maybe a little bit too sure of themselves and too confident."
Sound like you?
11 SIGNS YOU'RE A XENNIAL
1. You didn't get your first mobile phone until your late teens or 20s, and it was a brick
2. You used a dial-up modem for school or university work
3. You watched Fresh Prince of Bel-Air, My So-Called Life and Friends on TV
4. You seminal movies were Heathers, The Goonies, Jurassic Park, Clueless and Empire Records
4. You loved Nirvana - but were too young to ever see them live
5. You had a strong allegiance to either Oasis or Blur in the Britpop era
6. You downloaded music on Napster
7. You had a MySpace, ICQ or MSN Messenger account
8. You made mix tapes on cassettes, and you owned a walkman
9. You had or still have a hotmail account
10. You can remember when you first heard about Google and Facebook, but there was always internet - even if it just contained an encyclopaedia
11. You listened to Blink 182, Incubus, The Offspring and Spice Girls
