Common misconception. As Philip points out, Al is only covered if he's making fun of the original song. "Smells like Nirvana" is a good example of a parody that didn't need approval (but Weird Al did anyway cuz he's a nice guy)
> Al is only covered if he's making fun of the original song
My only nitpick is to remove the word "only" because there is at least one other possibility where he's "covered" in the sense of not legally needing permission: whenever his work falls short of copying the words and/or melody of the original song. If he modifies the melody enough (there's no specific threshold, but let's say he avoids a run of 4+ notes with intervals identical to the original work) and also doesn't copy lyrics or any other copyrightable aspects, then he's covered. It's very possible to achieve a song that makes your audience know exactly what you're going for, without copying any of the copyrightable aspects: you can take the chords, rhythms, instrumentation, accent, etc.
In the case of Smells Like Nirvana, he takes the copyrighted melody, which would require permission but for the exception you pointed out.
