There are many definitions of fake news, but the topic is a rapidly developing one and not easy to summarise. Here is one attempt:
Fake news" is "fabricated information that mimics news media content in form but not in organizational process or intent. Fake-news outlets, in turn, lack the news media's editorial norms and processes for ensuring the accuracy and credibility of information. Fake news overlaps with other information disorders, such as misinformation (false or misleading information) and disinformation (false information that is purposely spread to deceive people).
Lazer, David M. J. et al., "The Science of Fake News," Science 09 Mar 2018: Vol. 359, Issue 6380, pp. 1094-1096.
Clickbait is probably the most easily recognisable fake news. Readers are lured into reading the story by sensational and misleading headlines and/or pictures only to discover the story doesn’t live up to the promise and be bombarded by adverts.
Labelling accurate sources and reports as "fake" has become an easy way to dismiss actual news. It has become a lazy, way of saying "I don't like this", "I don't believe it", or "I disagree with that" . This is in turn makes it harder for people to distinguish the facts from fiction and distinguish genuine news from satire and parody. Although satire and parody are sometimes called fake news they do not deliberately set out to confuse or mislead the reader or viewer, instead they mock current events and news media for fun.
Read more at: Fake news glossary: Top 10 words to know , BBC, 4 Aug 2020 (Links to a different site)
Image 'Fake news' by Markus Winkler