Two "Sides" of a Song
It is important to note that when using a song, there can be two separate copyrights involved. These are referred to as the two "sides" of permission needed. There's the musical composition, which is the intellectual property of the composer(s) who created it, or their publisher(s). It includes aspects like the lyrics, melody, rhythm, and harmony. Then there's the sound recording, which is the physical and digital property of the recording artist or recording label that produced it. Each one is separately protected under copyright. In some cases, they may be owned by the same rightsholder, but generally you will need obtain permission from two separate parties to use the full song.
Any time you are using a song's sound recording, you are also using the song's underlying music composition.