Only a court is able to rule on whether something is Fair Use or not. Generally, a parody must take aim at the original work that you are parodying.
Here are some tips on how to figure out if your parody is indeed a parody:
- If the parody takes aim at the original work or artist, it is more than likely Fair Use and a legitimate parody (ex: "Perform This Way" by Weird Al takes aim at Lady Gaga's out-of-the-ordinary costumes)
- If the "parody" just changes the lyrics and does not reference the original work, it is more than likely not a parody and is instead a derivative work. This would require direct permission from the publisher(s). (ex: "Another One Rides the Bus" by Weird Al doesn't refer to the original "Another One Bites the Dust" or Queen at all. Weird Al just changed the lyrics of a song to be about riding a bus)