"Fake News" is a useful term and more specific and a bit different than "lie".
First of all "Fake News" can refer to either the source of lies, as in:
CNN is fake news
Or may refer to a specific proposition told by the source of the lies as in:
CNN's latest report is fake news.
On the other hand "lie" may be used as a verb as in:
CNN just lied again.
But we would not use "fake news" as a verb. Nobody says:
CNN fake news'd again.
Nor do we use it with "told" as in:
CNN told another fake news.
And although the term "lie" is similar to "fake news" in that they are both sometimes used to mean an untrue proposition, the term "lie" implies the teller of the lie knows it to be wrong. "Fake News" just implies that its false.
Also "lie" is not used to refer to the source of the proposition like "fake news" is. For example if one were to say:
CNN is a lie
Its most plain meaning would be that there really is no such thing as CNN. It would only mean CNN tells lies as a kind of poetic metaphorical use.
And finally, "fake news" is limited in scope to sources of journalism or propositions from sources of journalism, where the term "lie" applies to everyone who says something untrue.