A parody is a work of literature, poetry, drama, music, or even film, which seeks to mock, another text. Culturally speaking, parodies usually seek to be relevant to a modern audience and speak a common (though not always popular) opinion. As a result, very often, the parody becomes more popular than the original work it pokes fun at. Cervantes' Don Quixote is one such literary parody. Most assume it is either original or simply poking fun at typical knights tales, when it was directly inspired by a specific story: Amadis de Gaula.
Many of Shakespeare's plays are parodies of other lesser well known works that would have been popular in his time, as well as parodies of common behavior of royalty and the rich. Even his poetry, such as Sonnet 130 ("My Mistresses Eyes are Nothing Like the Sun") are directly poking fun at typical love poems from his time and before.
Today, the popularity of literary parody continues with publications such as The New Yorker, but the most prominent form is found in television and film. Consider Saturday Night Live as one ongoing source of popular opinion and comedy through parody. The "Scary Movie" series seeks to parody popular horror films which all came out at the same time (parodies films like "I Know What You Did Last Summer" and "Scream").
Finally, even social media and popular internet sites are becoming parodied. Facebook was recently in a legal proceding with the creators of "Lamebook.com," over the use of what Facebook considered an infraction on a trademark logo and name. Lamebook ended up the victor and was allowed to keep its name and logo on the premise that Lamebook seeks to "parody" Facebook and is an obvious display of direct humor, rather than slander.