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By definition according to dictionary.com, Folklore is the traditional beliefs, legends, customs, etc of a people, lore of people.

Another quick definition is from afsnet.org saying that folklore is the traditional art, literature, knowledge, and practice that is disseminated largely through oral communication and behavioral example.

Some examples of American Folklore are the stories of Bloody Mary, Bigfoot, and Santa Clause. For Japanese examples there are Kitsune's, which are foxes, The Ghost of Oyuki, and many more.
The television show Supernatural has a lot of great folklore within its shows. From more common known stories like Bloody Mary and Sirens. One of my favorite episodes though is when they explore the Leprechaun folklore. Typically when you think of a Leprechaun you think of a tiny man with red hair all dressed up in a green suite looking for his pot of gold.

Supernatural's version morphs the typical idea and turns them into something more dark and sinister.
"A leprechaun is a type of fairy in Irish folklore. They are usually depicted as little bearded men, wearing a coat and hat, who partake in mischief. They are solitary creatures who spend their time making and mending shoes and have a hidden pot of gold at the end of the rainbow. If captured by a human, they often grant three wishes in exchange for their freedom.

The leprechaun originally had a different appearance depending on where in Ireland he was found. Prior to the 20th century, it was generally held that the leprechaun wore red, not green. Modern depictions of leprechauns are largely based on derogatory 19th-century caricatures and stereotypes of the Irish."
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