The word is defined as "a significant cultural, political, or social change arising from the actions or influence of young people".
It first rose during Britain's June general election, which saw an upsurge in youth turnout, then had an even bigger spike in September around New Zealand's general election.
However, the word was first coined in 1965 by the then Vogue magazine editor Diana Vreeland to describe how youth culture was changing fashion and music.
It beat eight other words on the shortlist.
These included "milkshake duck", a "person or thing that initially inspires delight on social media but is soon revealed to have a distasteful or repugnant past" and "white fragility", defined as "discomfort and defensiveness on the part of a white person when confronted by information about racial inequality and injustice".
Also shortlisted was "broflake", a man who is readily upset or offended by progressive attitudes that conflict with his more conventional or conservative views, and "newsjacking", defined as taking advantage of current events to promote a brand.
Casper Grathwohl, president of Oxford Dictionaries, said Youthquake was a word everyone could rally behind.
"Youthquake may not seem like the most obvious choice for Word of the Year, and it's true that it's yet to land firmly on American soil, but strong evidence in the UK calls it out as a word on the move," he said.
"We chose youthquake based on its evidence and linguistic interest. But most importantly for me, at a time when our language is reflecting our deepening unrest and exhausted nerves, it is a rare political word that sounds a hopeful note."
"We turn to language to help us mark where we have been, how far we have come, and where we are heading," Oxford Dictionaries said.
Youthquake best reflected not only the ethos, mood and preoccupations of the past year, but had "lasting potential as a word of cultural significance".
The other shortlisted words are antifa, gorpcore, kompromat and unicorn, something dyed with rainbow colours or decorated with glitter.
Previous words of the year include "post-truth" (2016), the "face with tears of joy" emoji (2015), "vape" (2014), "selfie" (2013), "omnishambles" in Britain and "GIF" in the United States (2012) and "squeezed middle" (2011).
Published : December 16, 2017
By : Agence France-Presse London