Suspiciously Similar Song

See, their song goes "ding-ding-ding da-da ding-ding/ding-ding-ding da-da ding-ding", and mine goes "ding-ding-ding da-da ding-ding/ding-ding-ding-ding da-da ding-ding".
It's totally different.

—Vanilla Ice, comparing his "Ice Ice Baby" to Queen's "Under Pressure"

Want to use a popular song for your soundtrack, with or without the original lyrics, but don't have the money to get the rights? You can always get some studio musician to record a Suspiciously Similar Song -- an instrumental version of the tune with a note tweaked here and there, designed to sound as much like the original as possible while being different enough not to violate copyright.

Strangely enough, this sometimes happens with tunes which are clearly in the public domain in at least some countries.

A staple of shows that frequently feature parody songs or skits.

Note that, under United States copyright law at least, it is perfectly legal to use the same exact tune as the original song if the derivative work is clearly a parody of the original (parodying a work is a protected form of expression; using an original tune to parody something unrelated is fuzzier) -- though this did not become official until it was upheld a 1994 court ruling, and would obviously not apply to instrumental versions or songs that were instrumental to begin with, hence most of the examples on this page.

Contrast with In the Style Of where the song is covered, in a style as far from the original as possible. When one song recycles the tune of another it's To the Tune Of. In the music industry, this is called "Sampling", and usually requires permission...but it ain't always given. Basically Captain Ersatz or Expy for music pieces.

Note that if you're just reworking your own theme, that doesn't count since it's your own copyright you would be violating. And nobody cares about that - let's not go ballistic here.

Examples of Suspiciously Similar Song are listed on these subpages: