Why is #oomf so popular online?
There is an enigmatic hashtag - #oomf - that repeatedly trends on social network sites, and in particular Twitter.
It has been used more than 150 million times since it first came into being, in the spring of 2010.
But what does it mean? And why do people use it? #BBCTrending investigates.
Archive courtesy British Pathe
Produced by Dougal Shaw
All our stories are at BBC.com/trending
- From the section Magazine