Satire sites create fake news stories with a comedic bent that parody current or historical events and mimic the format and style of actual news stories and opinion pieces. Frequently, these stories are so convincing that readers will share them as "real" news on social media, and some satire stories have even been cited as real by politicians and within the media. The most famous such site is The Onion, but others include the feminist-themed Reductress, the politically-oriented Borowitz Report, and the punk rock Hard Times.
Wikipedia maintains a list of current satire sites. If a news story seems too absurd to be true, check its source and cross reference it with this list--it just might be a joke.
Wikipedia's List of Satirical News Websites