The father of trending: Abdur Chowdhury
It's one of those internet phrases that have seeped into everyday usage.
Newsreaders tell us a story is trending, editors tell their staff they want interviews to trend and activists want their causes to trend.
The goal for many news organisations today is to have their content shared so widely, so quickly and across so many platforms that it takes on a life of its own, achieving a sort of uber-ubiquity and eventually the hallowed status of "viral".
But how did asking "what's trending?" become such a pervasive online trend?
Facts v Feelings
To get to the roots of trending you have to go back to late 2006, when a group of engineers in the US state of Virginia, founded a company called Summize.
At first glance the start-up's website looked like any other search engine. But while Google and Bing focused on facts and figures, Summize was being more touchy-feely.
"We had a premise that real-time summarisation and sentiment analysis were important - looking at how people feel about a given topic," recalls its co-founder and former chief scientist Abdur Chowdhury.
"Often, we can pull out an exact date like when was Abraham Lincoln born - it's very factual - but [not] how do you feel about the weather?
"Or how do you feel about this political topic or that?"
In the mid-noughties, social media sites were still a bit of a novelty, so for answers to those questions Summize first turned to more traditional sources of online opinion including product reviews and blogs.
Mr Chowdhury and Summize's chief executive Jay Virdy soon noticed that when it came to opinions, there was one site that was fast becoming a global repository: Twitter.
They directed their technology at the platform and quickly saw results.
"Within six weeks we were doing over a million queries a day," Mr Chowdhury says.
"The hot thing at that time was the iPhone. You could see everyone's opinion and what they were saying about the iPhone in real-time."
Once it became clear that Twitter's content and Summize's technology were a good fit, a union between Twitter's 12 employees and Summize's six was inevitable, added Mr Chowdhury.
In 2008, Twitter acquired Summize and in the process users finally got the ability to search within Twitter.
Trending and hashtags soon followed.
Mr Chowdhury became Twitter's chief scientist and although he cannot recall exactly when or who coined the term, he remembers well the moment he realised trending was going to be big.
"I was taking the train and I said: 'Let's see if we can put together an algorithm to really figure out what people are talking about,'" he said.
"And so I started pulling out the people, places and nouns that were being discussed on Twitter."
Mr Chowdhury stressed that his original algorithm concentrated on spikes in the conversation.
"People are always talking about Apple or McDonald's or the BBC, but what you really want to know is did that deviate?" he explained.
"Is it way more than expected?
"As I'm taking the train ride and I'm watching the nouns coming out, I start to see Rome, Prague, London, Moscow.
"What I realised is that I was watching the Olympic torch runner run through Europe. It was at that moment I realised that trends - this ability to extract what's new and interesting happening in real-time - was going to be a thing."
Mr Chowdhury welcomes the fact that trending has broken out of Twitter and been embraced by other sites. However, he feels a little of his original vision has been lost along the way.
"Trending today seems like someone looking for interesting content to push up at the top, not necessarily something that the large majority of people want to talk about at the moment," he said.
The columnist and magazine editor Ann Friedman writes about journalism and technology. She says that trending has opened mainstream media's eyes to stories that would otherwise have been missed.
"I'm not so pleased with the trending era that I think every trending topic should be the equivalent of front page news, but I think editors tend to miss some things - they're not the most diverse group and stuff like trending topics and hashtags can really bring something to their attention," she said.
"I like to see reporters pushed by readers. To me that's good for journalism."
In September 2011 Abdur Chowdhury left Twitter after what he called an "amazing experience".
But his contribution has not been forgotten.
Last month, on the day of Twitter's 10th anniversary, Chowdhury got a personal and very public thank you from the man who'd bought Summize eight years previously.
"Thank you @abdur for being the coolest scientist I know and for building Twitter search and Trends," posted the social network's chief executive Jack Dorsey.