They just take a song, modify the melody a bit and render a much more professional and sofisticated sounding version? As an example George McRae vs. Abba:
George McRae: Rock your baby (1974): https://www.youtube.com/watch?v=kDD5BQlv8iw https://www.youtube.com/watch?v=kDD5BQlv8iw Abba: Dancing Queen (1976): Abba - Dancing Queen https://www.youtube.com/watch?v=xFrGuyw1V8s https://www.youtube.com/watch?v=xFrGuyw1V8s Abba - Dancing Queen https://www.youtube.com/watch?v=xFrGuyw1V8s Music video by Abba performing Dancing Queen. (C) 1976 Polar Music International AB View on www.youtube.com https://www.youtube.com/watch?v=xFrGuyw1V8s Preview by Yahoo
