urban legend

noun

1. a modern story of obscure origin and with little or no supporting evidence that spreads spontaneously in varying forms and often has elements of humor, moralizing, or horror:

   Are there alligators living in the New York City sewer system, or is that just an urban legend?

Word History and Origins

Origin of urban legend¹

First recorded in 1970–75

Example Sentences

The 1992 film sees Todd's character accidentally summoned to the real world by a graduate student in Chicago intrigued by the urban legend of the Candyman, setting off a chain of murderous events.

From BBC

It's one of London's urban legends that an American entrepreneur once thought he was buying Tower Bridge, but purchased London Bridge instead.

From BBC

Ms Powell adds that urban legends widely shared on the internet have "become their own form of folklore," adding: "I don't think something has to be supposedly 1,000-years-old to have any value."

From BBC

Then there is a multitude of straight-up urban legends or even fictional novels cited as if they are fact.

From Salon

These stories have all the earmarks of urban legends...The stories told about eaten pets are spread by word-of-mouth, and are unauthenticated by actual, traceable details.

From Los Angeles Times