Its definition is unclear and can change depending on whom you ask. It is used in increasingly politicised ways across much of the world.

And, although its leap to prominence is largely due to 140-character Twitter posts coming out of the White House, it now has widespread implications for journalism, politics, and how people everywhere share information online.

But what exactly is "fake news" and what effect is it having globally?

"I think there is a fundamental problem that fake news became a catch-all term to mean anything that we don't particularly like to read," explained Alexios Mantzarlis, who heads the international fact-checking network at the Poynter Institute.

Mantzarlis told Al Jazeera that the term "fake news" was originally used to refer to stories that were entirely fabricated, largely for the purposes of tricking Facebook's algorithm to reach a larger online audience and generate more advertising revenues.

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But fake news gradually shifted to describe "any kind of myth or disinformation", Mantzarlis said, and it has been co-opted by US President Donald Trump and his supporters.

The Trump administration has used the term "fake news" to describe media reports it doesn't like, or articles that question the veracity of the president's statements, or that portray him unfavourably.

Trump himself has levied the label at CNN, NBC News, The New York Times, and other mainstream, US media outlets, and often in the form of an all-caps zinger at the end of his infamous Twitter posts.

Fake news became a catch-all term to mean anything that we don't particularly like to read. Alexios Mantzarlis , Poynter Institute's head of fact-checking

According to Piers Robinson, a professor of politics, society and political journalism at the University of Sheffield in the UK, much of the debate over fake news revolves around being "in a post-truth environment where anything goes, and [where] alternative media and politicians, such as Trump, are wilfully engaging in misleading, deceitful and deceptive political communication".

But while it has been packaged in a new and highly politicised way - especially following the US election and concerns in Europe over Brexit - the manipulation of information by politicians and other actors has been around for some time, Robinson told Al Jazeera.

"It's selection of information, exaggeration, and omissions, which when you put them all together, means you have quite a deceptive picture of what is going on," he said.

This phenomenon is also not confined to the United States alone.

Fake news: A global phenomenon

Mantzarlis explained that about half of the most widely shared stories on Facebook on the eve of a referendum in Italy last year were false, and that fake news has been particularly harmful in the Philippines, where it is "poisoning online information".

Recently, The Manila Times columnist Yen Makabenta accused Philippines President Rodrigo Duterte and his predecessor, Benigno Aquino, of bringing the country into "the age of post-truth politics".

"The two presidential luminaries have midwived this development with a cascade of fake news, fake facts and alternative truths that, perhaps not surprisingly, has earned the Philippines the distinction of being the country where people have the least trust in each other," Makabenta wrote.

The problem has become so pronounced that the University of the Philippines launched a web-based, educational television network earlier this year with the expressed purpose of fighting disinformation.

Bruce Mutsvairo, a Northumbria University professor who specialises in political participation and digital journalism in sub-Saharan Africa, told Al Jazeera that audiences in the region have also become accustomed to distortion in the media.

He pointed to repeated rumours that have been circulated in the press about the death of Zimbabwe's long-standing president, Robert Mugabe, as one example.

More recently, several journalists at Tanzania's state-run broadcaster, TBC1, were suspended after they relayed a fake news story that claimed US President Trump had praised Tanzanian President John Magufuli.

"I think journalists need to understand the era that we are living in," Mutsvairo told Al Jazeera. "So, if we are talking about substantiating stories … then, maybe now, you actually have to do it twice, just to be sure."

He said that news consumers in countries with free public spheres generally tend to be more concerned about fake news and media credibility, and will actively seek out the truth.

Inversely, in states with less freedom, fighting fake news may be less of a priority.

Fighting disinformation

But fears that fake news is having an effect on political outcomes in European countries, especially those holding elections this year, like France and Germany, has prompted calls to action from European officials.

Andrus Ansip, vice president of the European Commission, recently warned Facebook and other social media sites to take stronger action against the spread of fake news on their platforms.

To fight such propaganda, to fight such fake news, we need to invest in journalism. We need to invest in media pluralism. We need to invest in media literacy. Renate Schroeder, European Federation of Journalists director

The European Union also announced it would devote more money and resources to its East Stratcom Task Force, which works to combat fake news allegedly coming from Russia.

The culture, media, and sport committee in the UK parliament has launched an inquiry into the effect of fake news on democracy, while the German justice minister has proposed fining social media websites if they do not remove fake news content or hate speech from their platforms.

But Renate Schroeder, director of the European Federation of Journalists, said countries "should be extremely prudent" and seek to balance freedom of expression and freedom of the press with combating hate speech and fake news.

Any effort to regulate social media should not go too far, either, since it can lead to censorship, she said.

"Our view is [that] to fight such propaganda, to fight such fake news, we need to invest in journalism. We need to invest in media pluralism. We need to invest in media literacy," Schroeder told Al Jazeera.

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She added that the effect of fake news is compounded by how quickly it spreads on social media, and by long-standing problems plaguing media organisations around the world, including budget and job cuts, a failing business model, and the public's growing distrust of the press.

Trust in media plummeting

Only 32 percent of people in the US said they had a great deal or a fair amount of confidence in the media "to report the news fully, accurately and fairly" in 2016, according to a Gallup poll. That is the lowest level recorded in Gallup polling history – the question has been asked annually since 1997 – and eight points lower than in 2015.

Trust in media declined overall across all EU countries in 2015, a European Broadcasting Union survey also reported.

Mantzarlis of the Poynter Institute said that to fight the fake news phenomenon, journalists should promote greater transparency in their work, and develop a robust corrections policy when mistakes do occur.

That may include "making [corrections] more detailed, explaining why the error was made, who made it within the newsroom, and how exactly the existing procedures failed," he said.

Schroeder added that the focus on fake news could potentially serve as a catalyst to reinvigorate the field of journalism.

"If we want journalism to continue," she said, "we have to invest in quality journalism, we have to invest in investigative journalism, but also we have to find new models for media to continue because the old traditional models are over."

According to Robinson, journalists should be using the fake news crisis to think of ways to strengthen the autonomy of the press, and make sure they are fulfilling their duty as a check on power.

Recent history has shown that when journalists fail to do that, the dissemination of false information can have harmful and even deadly consequences, he said.

That includes mainstream media outlets that reported a non-existent link between Iraq and weapons of mass destruction in the lead-up to the 2003 invasion of that country as fact, or people and organisations downplaying the effect of climate change.

"If you have situations where you have propaganda and manipulation and deception, and if you have a media which is not very good at correcting that or preventing politicians from engaging in that, this ultimately becomes corrosive on the public sphere," he said.

"Democracy was something that had to be struggled for, fought for over a long period of time … and I think it can be lost easily and it can certainly be lost in these situations that we're talking about."