Fake news has been used widely to describe a number of different kinds of news. Here's a breakdown:
1. Hoaxes/Completely Fabricated Stories Presented as News: This is what librarians would describe as fake news. These stories are unverifiable--meaning you can't confirm them in another reliable source, the sources often can't be confirmed, and the authors not qualified journalists or experts (they might be bots or have fictional names). The sites are often designed to make you think they are news sources. Examples: realnewsrightnow, abcnews.com.co, Internet Chronicle, newsbiscuit.com and a classic example from 1862 that fooled major newspapers.
2. Satire: Sites like The Onion, which claims to be the "world’s leading news publication," with a readership of "4.3 trillion." Obvious exaggerations reveal their satirical status. Headlines are generally humorous or outlandish and provide a (generally astute) commentary on real news and information, but aren't intended as news. Other examples: The Daily Show and the New Yorker's Borowitz Report.
3. Mistakes/Misstatements: Unless the intent is to mislead or satirize, mistakes and misstatments aren't actually fake news. Every news organization makes mistakes. News is released at a breakneck pace, and mistakes are bound to happen. However, reputable news organizations correct their mistakes and publish corrections. See examples: New York Times Corrections Index and Reuters' policy on correcting mistakes.
Fake news is not a piece of information with which someone simply disagrees.
Or, develop your own list of trusted resources. The following are journalism awards that can point you to high-quality news sources: