In popular music, a cover version, or simply cover, is a new performance or recording of a previously recorded, commercially released song or popular song. It can sometimes have a pejorative meaning implying that the original recording should be regarded as the definitive or "authentic" version, and all others merely lesser competitors, alternatives or tributes (no matter how popular)
My favorite cover has to be either....
The Animals' Cover of "Please Dont Let Me Be Misunderstood
or
Goldfinger's cover of "99 Luft/Red Balloons
my least favorite would have to be
Bob Dylan's cover of "The Boxer" Sounds a bit like drunken rambling.