The problem is that "fake news" is undefined. It could be

     pure lies
     partial truth / known lies
     partial truth / unprovable assertions
     conjecture passed as news
     limited snippets biasing intended viewpoint
     commentary (Fox "news")
     Disagree with assertions
     Propaganda by state actor

And those are what I could think of in a few minutes. Worse yet, who's to be the arbiter of "truth"? What credentials do they have? And why would we believe them to be transparent with truthiness ratings? They will have bias - will we be able to discern? Doubtful.

The underlying thing, is that when things are bought to light, the truth surfaces. Yet now, the attack is on the very definition of "truth", playing the ultimate word definition game.

Of those, only the first two qualify as "fake news", i.e. false news. To claim that "real news" do not contain the rest is ludicrous.

You made my point, that the definition of "fake news" is undefined. Pretty much anything can be pointed at and yelled "Fake News". And that's what we're seeing.

Fake news is news that is fake -- aka entirely fabricated with no basis in reality. "13 Obama supporters arrested for terrorist plot"-- boom, just made that up. That's fake news. Anything with a basis in reality is not.

It's always hard to agree on a definition of fake news, but their tweets are well documented to be extremely biased these days - even the tweet linked above uses loaded language like 'neocon'.