"Fake news" was not a term many people used 18 months ago, but it is now seen as one of the greatest threats to democracy, free debate and the Western order.
As well as being a favourite term of Donald Trump, it was also named 2017's word of the year, raising tensions between nations, and may lead to regulation of social media.
And yet, nobody can agree on what it is, how much of a problem it is, and what to do about it. Here's everything you need to know.
The origins of fake news
Governments and powerful individuals have used information as a weapon for millennia, to boost their support and quash dissidence.
Octavian famously used a campaign of disinformation to aid his victory over Marc Anthony...